Sounds like I am the youngster here at 38. Until a month ago, I was in the best shape I've been in for a very long time. (I moved from Los Angeles and headed East a month ago. Riding and eating has been all messed up while I'm moving around). When I was in the Army, I was in great shape -- running, riding, and everything else Soldiers do to have fun.
I did my first MTB race last weekend and had myself handed to me. Learned lots. Am working on a rough workout plan to get me to some goals. Having specific, quantifiable goals is the hard part right now.
Alas, I'm still in better shape than most people. Should I be happy or sad?