Two things: (1) Spend a fair amount of time in the gym, and (2) go to physical therapy to cope with whatever parts of your body aren't 18 anymore. For me, like many guys, it's my lower back.
The first time I saw my physical therapist, Brian, he said my back pain was due to a lack of mobility in my spine, which was a function of a lack of mobility in my hips. So I guess that old song, ("Dem Bones," as it's known) about the hipbone being connected to the backbone is right. (Incidentally, it turns out that osteoarthritis in the hips is much lower in countries where they squat to defecate than it is here. I'm not saying you should tear out your toilet, but it sort of makes sense.)