I'd say it's a little of both. On a game like 007 GoldenEye (N64), people have been speedrunning the game for almost 20 years, and are now in their early or late thirties. But there are still younger people that are getting to the game just now and getting new World Record runs. And this is just one game as an example, every game is different.
https://rankings.the-elite.net/goldeneye