Before you get to Orlando for Video Armageddon the finals, you must first qualify at a tournament in LA or New York City. And before you can get there, you have to pass a Pokémon Video Game Showdown quiz on the official website.
To keep it from really being you vs. a bunch of kids, there are two age categories: one for people born in 1996 or later, and one for people born in 1995 or earlier. So you'd end up competing with -- oh, a bunch of 13-year-olds. There's no way to avoid it; if you want to be a Pokémon Master, you're going to have to make some kids cry.