It's not that you have nothing to do when you retire, it's that you lose the passion for doing them. The "reason" kinda disappears.

If you're single, rich and retired, you have about as much chance of pulling a hottie whether you can do a backflip or not, whether you have a six-pack or not, whether you learn a new language or not.

When you're 22, all these things make you stand out from the crowd and so you have a motivation for chasing them. When you're older, anyone you talk to has probably done the same stuff as you already. So now you just kinda hangout.