Yikes. Too late. :X Also...
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.
Quoted for truth. Not that anyone'll probably give it a second thought, but it's what happened to me. Except a lot earlier. Basically for reasons NatureKeeper said, but with a lot less perceived bitterness (I'd probably feel exactly the same a generation ago, though).
"Then why are you here, man?"
As a franchise, I'm done, I've been done, and I'm happy that I moved on. There's nothing that can pull me back into Pokemon as a franchise, because I just can't keep up, and I just don't care. As a meaningful part of culture, and shaping my childhood? I cannot ignore that.
For me, Pokemon isn't about the newest games, cards, anime, whatever. It's the interpretations of the Pokemon by others who were also shaped by it. There's a connection there. Pokemon as mascots have no value. In fact, they're bland by mascot standards (even Mickey Mouse has more personality than Pikachu). Pokemon as characters, and in a sense as an expression of that person's interests, sense of humor, and other things? I eat that stuff up.
Fan art, anecdotal blogs, comic strips, light hearted parodies*, non serious fan comics and animations, all that stuff. That's why I still love Pokemon. It doesn't matter if you stopped playing after Black and White or Red and Blue, fact of the matter is, if you let it, it's shaped a part of who you are, and that's why you'll always have fond memories of it, and want to share those with other people (who may just think like you do. Bonus, eh?).
*I cannot get behind the idea some people have that Pokemon + blue humor = entertainment. Learn to write better material, or look over some 4 panel comics at the very least so you know how to create a meaningful punchline. A Pokemon or trainer swearing is not funny in and of itself.