[gnode]

> It could simply be something within the individuals that drives them to become grandmasters that itself is what staves off the decline.

Or it could just be survival bias. If your mental faculties are in decline, then you would be disinclined to continue competing in chess. I can imagine people would stop competing at that level long before they completely lost their marbles.

[TangoTrotFox]

People generally reach grandmaster when they're very young and I'm not restricting my statement to only those that continue to play in international tournaments. One may retire from high level competitive chess, but people rarely give up the game altogether.