Hmm.. I got 20 years to catch up.
40 isn't that old. My grandpa can still beat me in arm wrestling, well, he cheats using chi a lot, but oh well, and he still kicks my ass in Tai-chi. (well, 1 battle can last a day with his tempo).
40 isn't much, it's just 40. Most of my ancestors lived to 80+ except those that got blown to bits during Vietnam (sad part in my family history) and most of them are still alive and counting their money (Greedy [censored]).
Happy birthday, and don't worry about the age. Just worry about your health. Eat well and age slowly ^_^