I'm 20 since May, From Cork in Ireland and I rediscovered my love for Pokemon when I went back to college, then influenced my boyfriend to do the same. He's just turned 24 and a college graduate. I've just finished my first year there studying Psychology and I've always been a very good student. As far as being mentally challenged, I don't think I fit the bill.
In fact, in terms of Pokemon and most gaming in general, gamers seem to be some of the more intelligent people in the population in my opinion. Although that could be largely due to the socioeconomic background these gamers are from. I mean, to have video games you have to have money. Same with an education really. Mentally challenged is the complete opposite of what we are if you ask me.
And don't even get me started on the in depth game mechanics of Pokemon that even I don't understand. IVs, EVs, Contests, etc. It's crazy! No child of 3-10 could fully comprehend all of that to a standard that's actually useable in game!