You're never too old to start a fitness program. That's one lesson learned from Joy Johnson, an 81-year-old Californian who recently finished her 21st consecutive NYC Marathon in slightly over six hours. What shocks me is Johnson started a fitness program after retiring at the age of 56.

Her retirement walking program metamorphosed into jogging, running a 10K, then racing marathons -- all 50 of them. Johnson loves the energy running imparts. She can also eat whatever she wants, sleeps like a baby at night and confounded researchers at Stanford once with surprisingly good results on a bone density test. They thought the machine had busted.

If you've always been on the sidelines of fitness and your 40th birthday is a distant memory, it's not too late to start an exercise program. Preventive fitness programs are popular. In this article, USA Today highlights the benefits of senior fitness -- not only is the Silver Sneakers Fitness Program exploding nationwide, certifications for senior personal trainers are in demand, and one 2008 study found senior fitness lowered long-term health care costs.