Many of those are already at the peak of their ability, with no further potential.
I don't believe that at all. To reach your potential you'd have to get regular lessons and practice a lot. I'm a golf nut and I will never reach my potential because I have a life and don't have the time or inclination to practice enough to reach my potential. A lot of blokes who are off 28-36 would be retired and I bet they don't strive to improve. It's more likely that they just enjoy the walk. I know the blokes at my club just play for something to do. They have no interest in practicing.