What influences when characters unlock new limit breaks? I have Aerith at level 30 and she only has up to Breath of the Earth. In all the times I played the game, Aerith never had all of her limits at level 23. That seems highly unusual.

Also, yeah, why are people using Aerith to make physical attacks? First, she should be a healer and magic caster, and second, she should be in the back row because of her low defense stats and because magic doesn't care about distance. It's pretty silly that anyone would dismiss her for having a low attack stat.