Found this link through an exercise board I'm on, it's really fascinating. You put in your chronological age, answer a whole slew of questions about your health habits, and it calculates how old your body really is.
I'm 25.3, and the calculator said I was 20.3. Amazing thing is, the calculator said I was 16 until I answered yes to the question asking if I had any major job stresses or if I had moved in the last 12 months (twice, in fact!). That just blew me away!
So how old are you chronologically versus your real age?
Realage.com