I've had a Mage the entire game and it's never evolved into the next class. I'm sure it's the INT stat being to low, but god damn. Not that I"m missing them, I think the Mages are rather terrible in this game.Mages are quite strong, but sometimes a bad element can make their growth abysmal. Fire and Lightning mages are very powerful on offense. Try using an element changer and see if their INT changes.