>>29599463In-universe. There's enough evidence to say that ORAS occupies the same spot as RSE in the timeline, which was concurrent to the events of the Kanto-based games. Gens II and IV take place three years later, BW1 follows an unknown number of years after that, then there's two years from BW1 to BW2 and XY, and finally we have the years between XY and SM.
Note that the gap between II/IV and V needs to be long enough for 1) the last Rocket Grunt to move back to Unova and start a family, and 2) Caitlin to grow up and become an Elite Four member.
>>29599571Eh, Wally doesn't even look like he's aged three years since ORAS, so trying to estimate age based on physical appearance in the Pokemon world is a crapshoot at best.
