I can't remember exactly, but my characters were on level 55 or so when I beat the game. If you want a good place to level-up, go next to a save point and equip the ability that vastly increases the random encounter rate and keep fighting those enemies. I usually fought enemies that are quite easy to defeat but that still give a pretty good amount of EXP. I remember fighting a lot near Moonflow during Chapter 3, and I think I fought quite a lot of battles in the cave next to the Thunder Plains on Chapters 4 or 5. Finally I leveled up on the way to the Farplane.