Act your age! What, in the 21st Century, does that mean?

Shakespeare wouldn't know what to think: the seven ages of man he immortalised in verse over four centuries ago are no more. What with twentysomethings clinging to adolescence and sixtysomethings refusing to move gracefully to pensioner status, the new ages look very different from even a generation ago.

The changes, which have seen women delaying motherhood and men postponing leaving home, have prompted sociologists to draw up a new adulthood timetable – provided they make it: increasingly, it seems, people jump from childhood to kidulthood and progress no further.

A US-based developmental psychologist, who is leading efforts to analyse the new age groups, believes the twenties – which once saw adults married and saddled with a family before even reaching the halfway mark – should be viewed as the new life stage of "emerging adulthood".

Jeffrey Jensen Arnett, a professor of psychology at Clark University in Worcester, Massachusetts, thinks hitting 20 is no longer the gateway to becoming an adult, but is the start of a further 10-year journey to reaching that milestone. "I realised twentysomethings didn't fit into any of the traditional life stages," Professor Arnett said. "They were clearly different from adolescents, but they were not young adults either; they were somewhere in between," he added, comparing the new developmental phase with the emergence of adolescence at the turn of the 20th century. "Emerging adults are still making lots of changes, to their jobs, their love partners, where they live, and who with. They are not young adults because they have not yet settled into a stable path," he said.

Delaying adulthood has had a knock-on effect on other milestones, with 50 being declared the new 40, and 60 the new 50. Women strive to dress and look younger, while men take up extreme sports such as ultra-marathon running and mountaineering in an attempt to hold off Father Time.

Frank Furedi, professor of sociology at the University of Kent, blamed the prolongation of adolescence on a lack of "cultural affirmation" for adulthood. "The attributes of adulthood are no longer seen as a status symbol because adults try to escape from their own adulthood and become kids. All culture is youth culture," he said. "There are now books on quarter-life crises. When there's no valuation of adult status, then it's not surprising that it's not something people are anxious to achieve."

As life expectancy rises, delaying the task of growing up might appear a win-win situation. But there is a downside. "Infantilising young people has made them insecure. They are scared of relationships because they have an existential insecurity about becoming close," Professor Furedi said.

The IoS tested this in a snap survey of men and women from their twenties to their sixties to see how dramatically their lives have changed from those of their parents at the same age. The results are shown above.

The new ages of man (and woman) How lives and expectations have changed

MEN: 20s

Keith Robertson

Kitchen porter, 24, from Bristol

Keith earns about £13,000 a year and rents a flat with his girlfriend. His father, Lesley, 56, lives in Milton Keynes where he earns about £16,000 a year as a warehouse worker. He has remarried and owns a three-bed house.

"I never had a clear map of what I really wanted to do. I now work as a kitchen porter. I used to dress up as a fish in an aquarium, but stopped because I don't like getting punched in the genitals by little kids for the minimum wage. I have my own art studio. I work to pay for my art, but often feel emotionally drained after a long day. I live with my girlfriend. I don't think there is a stigma on unmarried couples living together like there used to be."

What did your father do in his twenties?

"My parents were married and living together by their twenties. My dad was a carpenter before working in a jewellery shop. My mum worked in a chemist and they lived in a flat. He now works in a warehouse. A real difference between the generations is education. My parents just worked and that's what was expected. Another point is family. Some don't bother with kids at all now; my parents had seven!"

WOMEN: 20s

Clare Waddell

Student, 20, from Liverpool

Clare is single and lives with her mother, Carol, 48, who is a full-time carer for her parents. Carol owns her terrace house.

"I study English at John Moores University in Liverpool. I want to be in a happy place with a nice job. Money is not so much an issue, and with the recession and Tories getting in, I don't think holding out for that is very realistic. I would feel happier if they were not cutting the number of police. Where I live is not exactly a leafy suburb, if you know what I mean. I would like to teach, a role that actually helps people."

What did your mother do inher twenties?

"I think my mum met my dad when she was 20 and she had me when she was about 28. She didn't go to university. After school, it took her a year to find a job. She worked as a receptionist at Johnsons the cleaners.

She quit when she had me and became a full time mum."

MEN: 30s

Justin Harper-Ronald

Call-centre worker, 31, from London

Justin is a former soldier and an architecture graduate. He earns about £14,000 a year and rents a flat. He has a long-term partner. His father, Ian, 66, is a pensioner and lives in Portsmouth. He and his wife own their home.

"I left the Army at 24, for health reasons. I got to see a lot but I also got shot at in Kosovo. In 2003, I decided on a complete change and studied architecture at university. I finished in May and I'm looking for work. Right now I work at a call centre but I'm eager to start out in my profession. I'm training for the Great South Run and I'm reading a lot too. I want to get back into rugby, which I played a lot in the Army. I don't drink as much as I used to, which can only be a good thing."

What did your father do in his thirties?

"My dad married my mother in his early thirties. My mum had four kids from a previous marriage; I guess that's something different. I'm looking to settle down with my girlfriend, but around this time my dad was taking on four kids. They had two further kids. Both myself and my dad were in the military, but there it ends."

WOMEN: 30s

Katharine Sanderson

Science journalist, 35, from Hereford

Katharine earns about £35,000 a year and lives with her boyfriend's parents. Her mum, Eileen, 63, is retired. She and her husband own their home.

"I did a degree at Imperial College and a chemistry PhD at Cambridge. I think I lived a different life to my parents, simply because I could. I was brought up by parents I was impressed by: I was never told to get married or have children and I've never felt they were disappointed in anything I did."

What did your mother do in her thirties?

"I was six when she was 35 and a mum with two children. On paper she was just a housewife, but she was doing lots. She trained as a teacher and taught at my primary

school. She had a husband, a house and children. I have none of those things."

MEN: 40s

Neil Townend

Company MD, 46, from Cheltenham

Neil is the managing director of a corporate entertainment company. He earns £40,000 to £50,000 a year and rents a detached house in the country with his girlfriend. His father, Alan, 74, is retired. He is married and has a house in Cheltenham and in Spain.

"I run my own business. I need to be fit and active. I love yoga, and I also go running and swimming. My girlfriend is younger than me - she's 26 and so I have to make sure I can keep up. I've travelled quite a bit to the Far East and New York. I also went to Ibiza. I did party there, but not too hard! I enjoy festivals, but at the same time I'd probably rather have a house party than go clubbing."

What did your father do in his forties?

"My dad also ran his own business but outside work things are different; the type of things I get up to he wouldn't have dreamt about. Last month, he and my uncle commented on how different I look from how they looked at my age. I think being active has a lot to do with that. His social activities revolved around drinking, gambling or golf. I learnt to cook after my divorce, I don't think dad ever cooked."

WOMEN: 40s

Karen Espley

Business consultant, 47, from London

Karen is self-employed and earns about £55,000 to £70,000 a year. She is divorced and owns her own flat in London. Her mother, Hilda, 68, is retired and lives with her husband in the house they own in West Sussex.

"I recently joined a software testing consultancy as a director. The money is not coming in so much right now but we recently got our first three clients. Essentially, it's something we are looking to grow and either sell it on or perhaps, if we decided we really love it, we might hold on to it. With people in the 20 to 30 age group, we found that their parents tended to settle down earlier. We have always lived an active life. I lived in Hong Kong for six years before leaving home, and I sail, paint in oils, and do a lot of skiing, mainly in Europe."

What did your mother do in her forties?

"She was completely different. She was what you might call a classic corporate wife. She got married at 24, and we lived in Ireland, Malta and Hong Kong. She was what people expected a woman to be back then. She did a lot of entertaining in the home, but she went back to part-time working, at a school library, when she was 45."

MEN: 50s

Richard Hunt

Company secretary, 58, from Portsmouth

Richard earns £40,000 as a company secretary. He is married and owns his own house. His father, Michael Penn Hunt, died two years ago aged 84.

"I trained as a company secretary for a car tyre company in Havant. I have been doing this for 23 years now. With the recession I'm just trying to survive and hope for a decent retirement. I do a lot of choral singing, bell-ringing, and some DIY. I went to Surrey University and while there I auditioned for the Guildford Choral Society. I met my current wife through the bell-ringing. We practise once a week and on Sundays – and, of course, at weddings."

What did your father do in his fifties?

"We had a family business that went bust in the recession of the 1980s. It was started in 1825 as a glorified builder's, outfitting offices in banks. But when that recession kicked in, people started to cut back on individual offices in particular. My dad got taken on by another company, fortunately, and bought a shell of a boat which he fixed up. It was a 40ft Moody, the only one handmade out of the Moody shipyards. He had an OK retirement when he did eventually retire on a state pension."

WOMEN: 50s

Helen Fellows

Retired, 52, from Portsmouth

Helen is a retired widow and lives in her own house in Portsmouth. Her mother, Dorothy is dead.

"About six months ago I took early retirement from IBM and spent last summer working as a windsurfing instructor at Poole Harbour. I ride a mountain bike and windsurf. I've travelled quite a bit in South America and been on ski trips and walking holidays in Europe and Africa. I was married but my husband died about 20 years ago. My life would have been very different if that hadn't happened."

What did your mother do in her fifties?

"My mother stopped work as soon as she got married. Some time in her fifties, my mum returned to part-time factory work. It was only in her sixties that she got into hobbies. She left school without any qualifications to look after a sickly parent. I've had so many more chances, whereas for my mum the only opportunity was to marry."

MEN: 60s

Charlie Pottins

Retired, 67, from west London

Charlie lives in sheltered housing on his state pension and his NHS pension. His father, Dave, is dead.

"I used to work as a storekeeper in a hospital in south London. I have been politically active since I was a teenager. I joined the young socialists in the 1960s and was active in the Socialist Alliance when it was around in the late 1990s and early 2000s. I spend a lot of time on the internet writing my blog or discussing on Facebook. Facebook is great for networking with people."

What did your father do in his sixties?

"I suppose in one way we are the same: he was a tenant of the same housing association as me, but they were in Manchester. He retired with both a Post Office pension and an Army pension. He took early retirement but started work again soon after as a filing clerk. He volunteered in an ex-servicemen's care home. He started going to the synagogue more, but I don't know if that was out of genuine belief or just as more of a social thing. My dad married late. Both my parents left school at 12 and started working because their fathers had died. My dad ended up in the Army and was in India in the 1920s."

WOMEN: 60s

Ulla Kite

Teacher, 63, from south London

Ulla teaches modern languages at Dulwich College, south London, but also has her state pension. She is widowed and owns her home. Her mother, Marlis Rolfe, is dead.

"I was born in 1947, in Germany, and now I teach at a private school. I came to England when I was 23 after I studied English, French, and German. I'm interested in photography and architecture. I travel a lot and I've just came back from China. My mother used to tell me not to travel but leave it until I was older, but she never really went anywhere herself. I'm interested in music: my late husband, Christopher, played the harpsichord, as do I, and I also play the cello."

What did your mother do in her sixties?

"My mother never really worked after having children. She was a private secretary before she had children and worked as a nanny. She worked for the German chancellor at one point, but after she had children she stopped and the war disrupted everything. Many of my family fled to the West when the Russians moved in."

Interviews by Daniel Read and James Burton