I'm 18 and I'm still liking Pokémon, and with the exception of a few years in between (when Digimon completely took over me), I have not stopped liking it since the age of 11. I'm not afraid to tell people that I like Pokémon; I wear my Pokémon t-shirt out, and everybody can clearly see it with their own eyes; once, after I brought a Pokémon publication, I went to the library to read some international newspapers. I placed the carrier with that publication inside on the table in the reading longue, in such a way that people could see it's contents. I didn't really care what other people might think of me; it's their own opinion. They can even mock at or laugh at me; I simply don't care about the contorted opinions of such people and just brush it off.
I once saw a group of teenagers (around my age) playing the Pokémon card game, and they were opening discussing strategies and such. In Japan, a survey revealed that 35.7% of Pokémon fans (in Japan, at least) were from the 13 to 15 age group, and 2.1% of them were aged 20 or above (fans aged 16 to 19 made up 9.6%) (I got these figures from that Pokémon publication I was talking about earlier, an offical publication). All these (plus the fact that there are quite a lot of members aged between 13 to 19 here, including myself) prove that Pokémon is not something childish or stupid; I see it as something that has mass appeal across ages, from children to adults. It's people who only can see the children group of the auidence, or just see only the surface of things, that think that Pokémon is childish and stupid.