RMXP levels go to 99. For 2k, the easiest thing to do would be to edit the experience curve so that it just takes longer to get to level 50. You can also make it so that enemies don't give much exp. You can also effectively increase level max by controlling exp and levels with variables once you hit 50. You won't be able to make it say that you are a level higher than 50 in the menu, but stats increases and stuff would show up. You could also make a Custom Menu out of events which could show it, but that is not easy if you are new to events, plus it is not as nice looking.