I've been with it for 2/3rds of my life, might as well stick with it. I may take breaks from it from time to time, but I always come back. If I keep enjoying the games and the show I see no reason to stop. (Plus I'm still waiting for an epic TR-showdown like they were originally planning to do in the first movie.)
I only just recently got into Pokémon--little more than a month ago--so I'm sure I'll keep liking it for years to come. Though when I grow into adulthood I'm sure it'll kind of fizzle out, but that'll likely only happen when I lose interest in video games. And I know for a fact the day I lose interest in video games will be decades from now.
Pokemon's got my love until it completely becomes Final Fantasy, maybe around VI/VII gen? Until then, I'll keep nostalgialating all over the franchise and the simpler days back 12 years ago, when the villains didn't want to end the world, and, 151 was the magic number.