Who needs a bus pass? Meet the silver sportsmen and women still going for gold...

Helmut Wirz loves to bungee-jump. The former pharmacist from Germany has chalked up at least 100 dives over 13 years. But what's most remarkable about Wirz is his age: he's 87 – and impressively fit.

While stereotypes of the elderly might persist, they're a world away from Wirz and his energetic band of karate-chopping, volley-smashing, Alpine-skiing fellow seniors. From Sister Madonna Buder, the 82-year-old triathlete, to Nick Bollettieri, the legendary 80-year-old tennis coach, the individuals on these pages are engaged in pursuits we're not accustomed to seeing pensioners take part in.

"I was looking at images of old people in magazines and saw only stereotyped pictures of smartly dressed sedentary people, or shots of the poor, decrepit, suffering elderly," says the German photographer Karsten Thormaehlen. "And as I browsed through these images I felt I was suffering with them." Which led Thormaehlen to scour the world for willing retirees who might provide a glimpse into another side of ageing; a counterpoint to the vast numbers of the superannuated who have been sidelined by ksociety. Shooting these exceptional pensioners, a mix of 25 active-sports enthusiasts and former professional athletes, for a series entitled "Silver Heroes", Thormaehlen also hoped to answer a question he had posed himself: "What can people do in old age?" The answer, as the series testifies, is almost anything, from skiing and mountaineering, to lifeguard duty. "From the very first individual I approached," says Thormaehlen, "I found these people to be confident, fun and energetic, and it was infectious."

The situation isn't quite as promising in the UK: a recent English Longitudinal Study of Ageing report revealed that about a quarter of all men and women aged between 50 and 64 struggle to walk more than 400 metres – a trend that significantly worsens higher up the age bracket. So, while people these days are living to an older age – a third of babies born today will live to 100, according to the Office for National Statistics – with our increasingly sedentary lifestyles, it seems we are poorly equipped to deal with this longevity.

Yet at least part of the answer to this demographic timebomb could be exercise. Countless research has suggested our quality of life can be hugely improved with vigorous exercise; a recent Danish study showed how, if a 50-year-old exercises four or more hours a week, they are a third less likely to suffer a heart attack by the time they reach 77.

Which brings us back to our band of seasoned adrenaline junkies. Thormaehlen's series has struck a chord with the World Health Organisation, whose latest campaign on ageing has used images from the collection in a bid to dispel stereotypes and promote a more active lifestyle among the elderly. And the poster boy for this campaign? None other than the bungee-jumping Helmut Wirz.

It's not just fellow seniors that this elite group inspires. "Working with these people made me feel old," says Thormaehlen. "I'm 44 and I'm not as active as they are." He tells of visiting one subject, a 73-year-old postal-worker-turned-body-builder. "As he was training, he asked, 'I can lift 120kg, can you?'" Thormaehlen couldn't, and it changed his attitude towards his subjects irrevocably. "I've become a new person since shooting this series," he says. "I no longer listen to prejudices concerning old age." You might imagine he'd also now be running several miles a day, like Sister Buder. "Actually, I'm still not going to the gym," he admits, "but I think about doing so every day."

'Silver Heroes' is published later this month by Kehrer Verlag (kehrerverlag.com). For more from the photographer: karstenthormaehlen.com