http://well.blogs.nytimes.com/2015/07/01/older-athletes-have-a-strikingly-young-fitness-age/

Older athletes can be much younger, physically, than they are in
real life, according to a new study of participants in the coming Senior
Olympics. The study found that the athletes’ fitness age is typically 20 years
or more younger than their chronological age, providing a clear inspiration to
the rest of us to get out and start moving more.