[Canon]

Actually there's an adult Eevee Eri too. He actually spent the majority of his time as an Eevee, and evolved so late he missed the chance to naturally learn Fire moves. Not that he battles anyways, but he gets a little embarrassed about it.

But that's neither here nor there.

Eri grew up around a bunch of Celebi, teaching him how to use his ability. He basically went to time travel school. His curriculum included self defense, control of time travel, history, an art of his choice (he chose culinary arts), diplomacy and negotiation and languages. A lot of languages. Since Eri's purpose in life is to travel through time to better his past lives he needed knowledge on a lot of things not normally present in a school.

Long story short, Eri was a pretty crappy student. He didn't have a way with words, was pretty quick to talking back and picking fights and never had the patience to learn a new language. He did "okay" in self defense at least. The only thing he really managed to do was control his time traveling. He basically graduated with the bare minimum needed. But really, it was almost impossible to fail. The moment you controlled your powers you were basically free to go.

He stuck around for "graduation" and then dipped. He did often skip class to visit a lovely Eevee gal though.