Honestly, I think the majority of the people that play nowadays, are the ones who grew up with it, and continued to love the games. I'm pretty sure Pokemon was at its peak around the second generation, and thus most people who play the games should be in their teens or adults, which seems to add up with the members of the Pokemon forums around. It could be that most of the younger players just simply don't know or don't care about forums, but I'm pretty sure it's mainly because Pokemon is getting kinda outdated. RPG's aren't generally that popular anymore, and more and more children are seemingly beginning to play FPS games and the likes, which kinda pushes games like Pokemon to the side. It's kinda weird, considering the games are targeted at the younger players, but it just doesn't seem to be those people who play them anymore :(
Personally, I've been playing the games since I was around 3 years old, and I'm guessing the reason I still enjoy them, is because Pokemon was one of the better games you could get at the time, and the experience wouldn't be as shallow as if the people had played the current time's modern games first.