As a 26 year old currently playing X Version (literally as I type this), my response would simply be:
"Tell that to over half the gamer lounge at the college I go to."
Alternatively:
"Can a 10 year old fully comprehend the logistics of EV training, IV breeding, egg moves? No. A 10 year old understands 'catch' and 'fight' unless they are taught about all these things by those who do it, who are mostly adults my age."
I think anyone of any age can learn anything beyond what a person is "supposed to learn" by a set principle or already existing belief or idea by set certain age, all you have to do is walk forward. This kind of thinking breeds the hate for pokemon, because you must do this by this age, etc, etc.