On Presentation Zen, a blog I've been following for years to improve my conference sessions, I found a post about Stephen Jepson. He's 72 years old, a retired college professor, and he claims that to keep being playful and moving "is the single most important thing to do to be physically healthier and smarter, regardless of age."
His story is very inspiring, so go on and read the article and watch the video clips!
My children have brought me back onto the playground and in teaching me how to have fun playing, they make me a very happy man.