What age do pokemon reach maturity? Are they like humans and reach maturity in their teens or more like animals and much earlier?

It really depends on the pokémon and your definition of “maturity,” anonymous. Assuming you mean “adulthood” or “age at which pokémon are ready to breed,” some pokémon, such as caterpie, can reach this point within months after birth. Others, such as members of the dratini family, may take years to reach that point, and rock-types such as geodude may take decades. Still others—namely the traditionally classed “baby” pokémon—never reach that point at all unless they undergo evolution first.

Generally speaking, though, the shorter the life span, the quicker a pokémon matures, and only a handful really reach maturity in their teens like humans do.