Sounds like you are determined to stay in good shape and that, to me, is the key. I am somewhere in my 40's and have been able to continue to work out for all of my many years flying. I make to the hotel gym no matter how tired I am at the time. After a few minutes, I am energized and the exercise seems to help minimize the jetlag. Diet is also a consideration in our job. Lay off of the high fat desserts and stick to the basic good salads, vegetables, and healthy main courses and you'll be healthy and physically fit for many years!