If there's a magic pill for staying youthful, it may be one that's hard to swallow: exercise. Daily doses have been proven to thwart a number of ageing factors—stress, obesity, heart disease, diabetes—and the longer you're physically active, the less you'll notice getting older.

The catch is that a 50-year-old's body is not the same as a 20-year-old's; you can't push it the same way you once did, nor should you if you want to keep it in working-out order. So listen to these coaches—they're talking not just professionally but also firsthand—on how to remain fit, and proud of it, through the decades.

Here's an easy guide to follow at every decade.