>>33366308>evolution doesn't define age in PokemonExcept, it kinda does. That's why Venusaur give birth to baby Bulbasaur, and a ton of Pokemon can't breed until they reach a certain evo stage. Most Pokemon evolve via experience, which is presumably gained by "training." In the wild, training is just them doing their natural thing—hunting, playing, swimming, sparring, etc. (Which is why one might find something like, say, an old, experienced Shiftry leading a clan of Nuzleaf.) Human trainers just help them achieve this faster. First stage Pokemon that still haven't evolved after a extended time are often looked down on by other Pokemon in some way, shape, or form due to their stunted growth. Such Pokemon may reach "old age" before they evolve, but this is rarely IF EVER touched on. Stone, friendship, and other such evolutions are the only odd cases.
GF, TPC, or whoever tf didn't really put much thought into this, because kids couldn't care less. It's an issue that comes with still having adult fans; we're the only ones who subconciously care to try to make logical sense out of this stuff and/or justify our reasons for still liking a kids franchise.