Don't bother. That's really not necessary.

See, at that point, you get Magicite, and Magicite makes stronger when you level up, so the more levels you gain holding Magicite, the stronger you'll get.

However, the eariest espers you get don't really do very much, and it's not like there's a noticeable difference by the end of the game if you suppress your level until you get Magicite.

So yeah. Don't worry about that. :P