Revisiting F3 on PS3 this time and level 20 seems to be as far as I can go....XP maxed. Why would my level "meter" show level 21 yet not allow me any further progress? Thanks.

You need the Broken Steel DLC. Without it, there is an ending to your story. You will have to stop, at a certain point, to avoid triggering the end of the game. With it, you can play on forever.

Thanks BD