FWIW, there are a lot of still relevant "older" players approaching their 40s in the fighting game community.
I would not be surprised if the 20-something pros in stuff like FPS games would still be quite good at them when they hit 60-- provided of course, that 1) life doesn't get in the way, 2) that they still playing the games regularly, and 3) that the genre even still exists at that point.
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I know one older gentleman playing a FPS. He is not very good, but better than the majority.
It's all about community though. If you play on the same server or a not-very-popular game, you would soon know all the "regulars". The actual game is there just to hook you in. You stay for the community.
I don't think the pros would be very good. If anything, I'm worried about how much carpal tunnel syndrome and other health risks they put themselves through by being pro.
It's my first time playing a proper FPS, yay Steam and Linux compatability.