Is Pokemon in general for little kids? Yes. Does that mean I'll stop playing because of that fact? No. Like a lot of people, I'm one of the older fans of the series, having been into since the GS era. I just turned 24 a few weeks ago, and have been approached many times by people I know asking me why I'm still into it even though it's so kiddy. Of course, there were times when my love for the series kind of dropped (most recently, the Diamond/Pearl release... They drew it out so much in the year or more beforehand, my enthusiam for the games was pretty much dead by the time they came out. Sure, they were good, but they started promoting the fourth generation almost a year and a half to two years before it's time...and it drove me nuts!).
In any case, I got into this mostly for the reason that it reminded me so much of all the old Super NES RPGs I used to play religiously as a kid (Final Fantasy IV, Final Fantasy IV, Super Mario RPG, etc.). So, I have to say, a lot of its nostalgic reasons why I've stuck with it so long, even though Pokemon is mostly for little kids. Besides, a lot of the older Pokemon fans get into a lot more adult stuff with their fan fictions, comics, and other projects, myself included though I exercise more restraint than others do (granted, they have little to do with the series itself aside from just being based on it, but I guess I just wanted to point that out).