> Ageism also just one of these shitty unproven biases

You might be right, if we were talking about anything except chess.

Chess, unlike everything else, has a clear ranking system and lots of records for people to analyze. And unfortunately, the record is very clear: chess ability decreases after a certain age.

However, the decrease is more likely due to stamina than mental decline. Chess tournaments take a long time, and stamina definitely decreases with age. However, pro athletes demonstrate that you can probably go until around your early 40s before it becomes a real issue.

Having said that, it will be interesting to see how this generation does in the blitz formats as they age. Those will be less dependent upon stamina and a better measure of mental acuity for chess.