A lot of the posts in here are over-exaggerating, but to be fair it's not really possible to give an accurate or proper response to this topic. You never know when you'll quit something, so all the "'til death" posts...they could end up quitting the franchise as early as next year.
I didn't think I'd quit early myself, especially since I was hooked with competitive battling, but it happened, and it was for the best. A cousin who's in college planned to stop before B/W's announcement but ended up getting the game anyway. (Though I think he stopped for good now. lol)
Honestly, and forgive me for saying this, but I think it's a bit silly to believe you won't quit at an early age, or ever, given that it's almost guaranteed you'd be busy with far more important things the more you grow up...well unless you're that gullible. And when you think about it, it's for the best. It's only natural as well, it's in the human nature to change interest and move on.
Basically, it's impossible to predict when you'll quit. However, I think a good question will be...should you lose interest or take a break, would you come back to it? That's something that's worth wondering about.