Is Use it or lose it by Peter Snell.

Peter is a New Zealander that won 3 olympic gold medals at 800 & 1500 metre in the 60's. He now is a Associate Proffessor at DEpt of internal medicine at Uni of Texas Southwestern. He is 70 this year, still working at the uni, looks 20 years younger and is still active & competitive in all sorts of sports.

Use it or Lose it explores the many mounting health problems and their causes & how you can use simple activites, exercises & plain commmon sense to take control of and enhance your life as you get older and approach 'Third Age'.

I really recommend reading it what ever your age