That's silly. Sure the #1 player is in their 20's. What on earth does that have to do with learning new things? The younger trend for ranked chess players likely has a lot more to do with the fact that there is almost no money it .
Since there are players that were world chess champions for spans of 20 years or longer, your logic makes sense. Since we are the same age, I don't believe your failing logic is a product of your aging mind.