Plus look at the number of NBA stars still at their peak late into their 30s
Most of them are far from their peak, but I get the point. The exact time of introducing a chance of retirement is up for discussion, I think. It could be 35 years (so already after the start of a decline), or even 38. Point is, we probably need some mechanism to make retirement automatic. If some players continue playing until late 40s, with some luck involved, so be it. But the majority should go at some time.
I have a legend of my club at 38 now. He still gets some playing time, and he could be really productive at a lower league. I know he will have to go, but I don't want to fire him. I would much prefer to have an objective random mechanism to declare that the time is up.