Leave the game? NEVER! I've invested too much time and money in this game to drop it cold turkey.
Now I've been playing it since it came out in 1999, and since then I've had.... at least two real girlfriends, graduated high school, started and dedicated myself to college (just started my third year at San Francisco State University), made several short films and worked on my own public access TV show, worked on several serious artists ventures, got and kept a good paying job at Longs Drugs (can't beat $9/hour at my age), traveled around the US several times and visited Europe, turned the legal age to both smoke AND drink (not that I do)... and other things that most "normal" people my age seem to do.
... I'm almost 22 now and I have no interest in leaving the game. Plus a lot of my real life friends have come from Pokémon... in fact a large CHUNK of them are Pokémon players (as opposed to people I've met from work, school, or elsewhere).
But think of it this way...
everyone has a non-career hobby they do on their off times. They're not insane about it, but it keeps them busy. And lots of times it could be as goofy or dull as the next thing. Say... Bird watching, insect collecting, Civil War recreation, model trains, or Barbie doll collectors. For me, I'm just a regular guy who's hobby just happens to be playing the Pokémon TCG. It could have easily been knitting or golf. And nothing says your hobby can't be Pokémon as well.
But I do want to touch on when you said this:
Some people are waaay dedicated to the game, and that just scares me. I don't want to become one of those people.
If you're talking about becoming one of those weird creapy gamer types who take their interests a bit TOO seriously... then I doubt you will with Pokémon. Thing is, playing games doesn't turn you into that type of person. If you don't have that mentality, then it just won't happen. Most people around the 'Gym is living proof of that.
But the beauty of this game is its nature... you play it just to have fun, and I think most Pokémon players understand that. I feel that BECAUSE Pokémon is a notorious kids game that players don't take themselves seriously when playing it. Therefore, you don't see a whole lot of those weird players in Pokémon as you would in Magic or Yu-Gi-Oh. Particularlly if players are JUST Pokémon players and not Magic/Yu-Gi-OH AND Pokémon players (and even then, those folk are the more easier going out of their other Magic/Yu-Gi-Oh friends).
I doubt you have ANYTHING to fear by playing Pokémon.
And there are plenty of older players who'll give you support if you need it (heck, sometimes we need it outselves!).