Hermit will be 54 next month.
That is my biological age. My metabolic age (I think that is what it is called) is about 15 years less.
In the book "Forever Young" by John Thomas he has a test to take to determine your metabolic age. I don't know how valid his test is but it is fun to take and gives you an idea of how one might be abusing their body and what can be done to improve your health.
Thing like stress, drugs, caffeine, tobacco, diet etc. all have an effect on how the body ages. If you can find the book, take the test and find out how old (or young)you really are.