As everyone will tell you, it isn't the capabilities that deteriorate the most, like beating kids in sprints, it's the recuperation time. I'm 60 and have experienced this in 5-year blocks. So every 5 years I'd notice staying hurt for longer which would make me slow down more to avoid it.

When I was in my late 40s I was playing a pick up basketball game. I was above the 3-point line. I guy tried to get past me. He had the opening but I put out my hand just to slow him down a slight bit. My pinky must have hit his arm or something. It broke (it was weak from a childhood injury). Anyway, I looked at my pinky at a right angle and it occured to me I must be getting old if someone knocking into it casually would break it. I laughed. You have to laugh!

Sometime in my 40s I stopped jumping for rebounds. Even if some would complain. Falling on someone's foot and twising my ankle would result in a few weeks recovery. BTW, I'm 60 now and the ankle I very seriously sprained when young is, I don't know how to put it, weaker than the other, floppy.

So be careful, injuries you get now will come back to haunt you, more and more.