The way you're meant to the play the game is to get around 8 levels in your pre-Jedi class then get to Dantooine and end up with around 12 Jedi levels when you hit overall level 20. However, it is possible to avoid levelling up at all (except for one forced level up) before you get to Dantooine, and end up with 2 pre-Jedi and 18 Jedi levels. That's how I normally play.