LONDON—At the ripe old age of 28, Patrik Sättermon considers himself over the hill as a professional videogame player.

"For some games you have to be super fast, and at 24 or 25 you're past it, you're a veteran," says Mr. Sättermon, a former world champion in the game Counter Strike. "You don't realize your reflexes start to disappear, but you see it on the scoreboard."

So...