According to the Real Age website (I found the link on digg.com) my real age is 29.2 (versus my actual age of 36) and my life expectancy is 80.8. The test considers a variety of factors like biology, heredity, and life style choices.
I think the 80.8 is a bit pessimistic for my tastes. Given advances in technology over the coming decades, I'm targeting 150 as a minimum. As for the 29.2 estimate for my real age -- I'm still holding on kicking and screaming to 27.
So, how old are you? Take the test here.