From Pathfinder Lost Omens Draconic Codex, which isn't enabled.

Mighty Dragonet

FEAT 1

You've grown especially large and now tower over your fellow dragonets. Instead of Tiny, your size is Small.

Special Though you can grow larger at a higher level than 1st, you can't retrain out of this feat.

Pathfinder Lost Omens Draconic CodexORC