>>25218751Like this guy says, OR/AS establishes that it and XY are different universes from everything that came before, with the big difference being the existence of Mega Evolution.
Right now I'd argue there are three groups or clusters of universes:
First cluster: Gen 1 and Gen 2
Second cluster: Gens 3, 4 and 5 (remakes essentially make it clear that this is a separate thing)
Third cluster: Gen 6 (Mega Evolution universe)
Each group/cluster of universes also contains lots of individual seperate universes (For example, we know for a fact that Black and White are alternate universes to each other)
>>25218762Considering that most of the child gym leaders at the PWT don't appear to have aged at all since Gen 3 or Gen 4, I'd say it's just Game Freak being lazy and not wanting to make new designs.