I'm 20, and from America. I personally have a few different opinions on the topic. The /games/ imo aren't to childish at all. You can tell pretty easily what video games are okay for your age group and what ones aren't. In fact, there aren't a lot of video games out there where you might find yourself going "wow this is... I need to not play this." hahah .
The SHOW might be a little more questionable. I wouldn't judge someone older for watching it but I really wouldn't watch it for the sheer fact that it, to me, is obviously for younger kids.
Collecting pokemon things is also something I find to be okay. Like, who doesn't want a flippin mudkip plush seriously .
I hope I helped a little. I'm tired I'm not even sure this makes sense xD.
I don't think it's childish at all, because there are shows meant to target much younger audiences than Pokemon. The adults that created the show had fun doing it, right? They weren't too old to enjoy the show, and neither is any other adult. My father is in his 50's, but he still enjoys watching so-called "children's" cartoons from his day. So, who's to say that all adults will see Pokemon as a show for kids? It's very famous and has come a long way since it's creation, and it must have gotten support from its fan base made up of all ages and all countries to help it grow.
the old seasons had real heart to them, about a child growing up and having to learn to let go of friends along the way. when he hurt, we hurt, when he showed loyalty we were encouraged. now in the current season the droll episodes consist of finding someone new, team rocket trying to steal them, failing, end of episode. if they brought back actual plots or continued development I'm sure I would get back into it. The comics themselves also touched on deeper issues such as death, loss, etc. so to answer your question the older seasons are more for adults, the routine stupidity that's on today is for children who don't know better