Just because you're getting on a bit, doesn't mean you have to hang up your trainers. Indeed, it's beginning to look as if 70 is the best age to hit the gym. Research published in the Archives of Internal Medicine suggests that taking up exercise after retirement can prolong your life, greatly increasing your chances of living until 90. And it's a movement with many believers. At Saga Magazine, we have a bulging file known as the Lycra Alert: people in their 70s, 80s and, yes, 90s, abseiling, deep-sea diving, jumping off cliffs and wanting to write about it.

"Exercise is the best investment older people can make," says fitness guru Joanna Hall, whose walking programmes (Walkactive.co.uk) are particularly good for the over-70s. "In fact, the older you are, the more dramatic the benefits you get from exercising." And it's never too late. "People who have never exercised before will get particularly good results," says Hall.

The secret for older exercise novices is to start within your capabilities, and move boundaries with your fitness level. Be it walking, the gym, Pilates or yoga, you need to push yourself but not punish yourself. And find an activity that respects your dicey bits: if your knees are wobbly, try swimming instead of walking.

Oliver Harte-Stockwell, a personal trainer with an older clientele, recommends "super-slow" exercise: slow repetitions using elasticated bands, stability balls and free weights, which build up lean muscle.

As at any age, the best exercise is a mixture of disciplines. Cardiovascular combined with flexibility disciplines such as yoga can help prevent falls - possibly the greatest danger to over-70s.

So the overall message is clear: find a few activities you enjoy, and keep active.

· The writer is the editor at large of Saga magazine.