The main reason pokemon is considered as childish game is because of the anime itself. Its geared for younger audience ages 7+. Sadly other animes they try to tone it down for younger viewers.

I can only tell two examples. Naruto and One Piece is suppose to aimviewers ages16+, which it is in Japan. However, American licensors are making it gear for KIDS ages 7 at least. Most violence, curses are changed/cut/editted out. Even some episodes are skipped and never aired.

It is for a fact though that pokemon from anime is generally aimed for kids, even in japan, not for older audience.

But since D/P came out, its the other way around. :) All the complex game mechanics they have implemented in the game. It impressed me and got me hooked. Feels like playing Red/Blue again. it seems that the game itself is meant for older players such as myself. I went to that gamestop tournament, and easily won up to semi-finals without any of my pokemon fainting, especially Porygon-Z,OUTRUNNING a rayquaza. However I lost at semi-finals :( Bad typing setup.By the way, I'm 24 :)