Olay. It would be very helpful if you elaborated, though. Are you telling me you really can rush through the entire game and not stop to grind quests even once, or is it more of a middle ground where you don't have to do everything but a little grinding is necessary?
It's trivially easy to be overleveled, due to the amount of sources EXP can be obtained from. Generally, you should accept sidequests whenever you see them, but not go out of your way to do them - most will autocomplete as you proceed normally. You'll probably only have to do a tiny bit of grinding, and even then probably just for one boss in the endgame.