Answer:
Here is a website that purports to calculate a biological age. They don't explain their methodology, but it seems to be calculated as something like: Your current age MINUS your personal life expectancy (estimated from your family history, health behaviors, etc.) PLUS the US life expectancy for a person of your age and sex . It is not clear how good the estimate of your personal life expectancy is, but my biological age is 10 years below my current age, so it must be right, right?
http://www.preventdisease.com/healthtools/articles/health_age.html