Pokémon isn't really aimed at a specific age-group, it's who chooses to play it and currently in this generation I'd say it is mixed. There are just as many teenagers - young adults who play as there are children, the reason behind this is because people like me who have played since the franchise first debut all those years ago are still sticking by it because of all those memories. There are popular games that appeal to a specific target audience, the likes of Call Of Duty, Halo, FIFA etc and sure they're popular amongst the teenager age group right now, however Pokémon still remains the second most popular franchise globally.
I'd say that the majority of older players that play are those who have been playing the games since they were younger, and now that Pokémon is still going strong after seventeen years, it's only natural to still have a strong following from a similar audience. Any newcomers are going to be kids because Pokémon is generally stereotyped for kids, but that doesn't necessarily make it true. To me, Pokémon is just a good (if not better) than any other gaming franchise out there, and as I've said in a previous post there should be no age limit to Pokémon.