Start getting ahead of the inevitable muscle loss and do some weight training. Don't be a gym rat, don't try to bulk up or get yoked -- just do some bench presses, seated rows, and kettlebell swings a couple of times a week. I'm 60 now and wish I had started this regimen when I was your age; it's unbelievably helpful to your cycling, your physique, your sex life, and your overall ability to postpone decline.