Mary Dejevsky: Don't panic. Britain is very far from being a Zimmer nation

We British have an unerring capacity to look on the gloomy side. And on no topic do we wax more morose, with more regularity, than on the ageing population. So the latest official projection, according to which one in five of us will live to celebrate our 100th birthday, is seen exclusively in terms of the burden we will place on the health and social services, not the triumph for first-world nutrition and medicine it truly is. As the scion of a family whose womenfolk have tended to live well into their eighties and beyond, I would say this is more good news than bad.

Which is not to say there is not bad news to be found somewhere in these figures. Of course there is, but it is not in the fact of an ageing population per se. It is in the implications for a society that privileges youth over age and has so far failed to come to terms with this particular demographic shift. There is no reason why living longer, by itself, should place a greater burden on public services. The health most people now enjoy in their fifties, sixties and seventies, and the active lives they are able to lead, would have been unthinkable even half a century ago. Our seventies are the new fifties. Why should our eighties and nineties not be the new sixties and seventies? Dependency, rather than longevity, might be a better gauge of expense to come.

We hear repeated warnings of the "ticking time bomb" of fractured thighs and dementia, and a remedy for Alzheimer's is proving elusive. But brittle bones can, to a degree, be prevented, and slowing, if not halting, mental deterioration is probably not out of the question. It remains that the last two years of anyone's life cost the state the most – at whatever age those two years come. That the number of people over 75 treated in hospital has risen faster than any other group over the past 10 years is as much a reflection on the poor provision for older people elsewhere – sheltered housing and the like – as it is on their actual need for hospital care.

What we are looking at today and into the future is less a problem of ageing, than of families and pensions. It is a family problem because in the past, many of those who survived to a ripe old age lived close to, or with, their families, whereas far fewer do so now. That reflects personal preference – that of the elderly people as much as that of their offspring – but also practicalities. Most of today's housing is not built for sharing across generations, and far more women, the traditional carers, are in paid work.

While there is poverty, much of it hidden, in the population of the very old, many of the "younger" old are not only active, but rather better off than in previous generations. They have strong ideas about the help they need and would be prepared to pay for it. But the state and the private sector have been extraordinarily slow to appreciate this new market and cater to its needs. Imagine if the sort of money pumped into Sure Start, nurseries and school buildings in the past 15 years had been spent on facilities for the over-70s, we might have not only more generous, but more appropriate and imaginative, provision that would moderate costs in the long term. More scandalously profiteering care homes would have gone out of business (or never been set up) and there would have been fewer expensive hospital admissions.

Pensions are an equally intractable problem. First, because the "system", such as it is, tolerates greater pension disparities than exist almost anywhere in the developed world. Those outside the millionaire bracket and the public sector have no certainty about their finances in retirement, beyond the basic state provision they will receive, and this hardly encourages prudent planning. The relationship between what people pay in and eventually get out is hopelessly capricious. No wonder they sought refuge and easy money in property, with all the market distortions that brought. And no wonder they demand "free" care, because they believe their national insurance and taxes have paid for it.

The greatest lag in state planning and public understanding, however, is the pensionable age. It hardly needs to be said that 65 today and 65 in 1948, when the state pension was introduced, are very different things. With foresight, the age might have been pegged to life expectancy, rendering unnecessary the sharp rises – to 68, and doubtless beyond – that are currently in the pipeline. But it should be clear to everyone that, if life expectancy continues to rise, we will have to work longer and work differently.

A little while ago the Government was widely ridiculed for suggesting a scheme under which volunteers might receive credits towards care-home fees in the future. But some more tailored system that encouraged, say, students and the "young" elderly to work part-time or seasonally – for pay – with the disabled or infirm should surely not be beyond the realm of possibility.

In short, an older, even much older, population should be no cause for panic. It should rather prompt congratulation and an enthusiastic search for new ideas. Anyone who doubts this should contrast, say, Japan (which is ageing gracefully, if disconsolately) and those countries, mostly in the Middle East and Africa, where more than half the population is under 25, under-occupied and a potentially destabilising force.

If you still question my equanimity about Britain's rising longevity, this postscript is for you. Cheer up! It may not happen. According to recently released figures from the (American) National Centre for Health Statistics, the United States registered a rare fall in life expectancy in 2008. In part, it can be put down to sharp disparities in healthcare, to diet and obesity, and to the increased number of first- and second-generation Hispanic immigrants who import the shorter life-expectancy of their homeland.

But the figures also show that it is among the white population of over-80s that life expectancy has declined most conspicuously, which is without precedent. One hypothesis is that the economic crisis harmed the ability of this group to fund their treatment and care. A more optimistic explanation would be that ageing finds a natural limit. Either way, if the US sets the trend, rather fewer than the one in five Britons forecast may be blowing out their 100 candles after all.

m.dejevsky@independent.co.uk