I kind of disagree on the chess player point. I think many older players would gladly keep competing on the highest level, but just can't keep up. It's not really far fetched that younger people think faster, have more stamina and can keep focus better in those several hour long matches in world class tournaments.

However, with older age comes ability to select where to focus better and put things in perspective. The skills gained with aging don't really help with chess, which reduces most of the time to raw calculation and focus.