I quit playing Pokemon when I was about 15. I told myself that I'd grown out of it, that I'd done everything I could in Gens I-III, and the prospect of games being remade made me feel a little disappointed. 'Why remake old games instead of coming up with new ones?' was my thought process at the time. That, coupled with an intense dislike for the fandom, meant it was relatively easy to cut Pokemon completely out of my life. And because I wasn't coming to PC, I never felt the need to check in on Diamond and Pearl, so those games completely skipped my radar until Lucario appeared in Super Smash Bros Brawl!
I only came back to Pokemon after my room-mate at university said he was going to get one of either Black or White. It turns out he didn't (and still hasn't!) but that sort of resparked my interest, and while I wouldn't say my love of Pokemon came flooding back. My desire to return to this place did. After buying Black, slowly but surely, all the good memories I had of playing the games started to return.
I don't think I'm as big a fan of the games now as I was when I was 10-or-so. But I do like them for what they are. I'll inevitably buy the next generation of games when they come out, but probably not as soon as they're released or anything. Life goes on, and preferences do change, like it or not. But I don't know when I'm going to quit. Haven't got a magic-8-ball for that.
Also, this is more a gaming question, so I'mma move it to PGC now.
Moving on up