Well I think there are many aspects that you have to keep in mind.
I am 23. If you take, for example, my generation, we all kinda grew up with Pokémon. I remember the breaks in school when I was about 9 and everyone was playing Pokémon or trading the cards. And as we all grew older, there were new Pokémon games and so I guess it's rather hard to get over something like Pokémon.
Of course, the anime is concipated for a younger audience, but the basics behind Pokémon do have the potential for much more mature contents than those presented in the anime. Plus, you have to keep in mind that it's possible to make quite a strategy game out of Pokémon, breeding them for IVs and doing CP. : D
So well, I think Pokémon is one of the few things that works with children as well as with grown-ups.