Nah, you should change the "Hero XP Gained - Creep Reduction Table" (in gameplay constants) and set it to 100, 100 (then you will gain the same XP from creeps 4 ever)
Or you could set it to 100, 98 (then the XP will decrease with 2% every level, so you can get to lvl 50 by killing creeps, but it will take a very long time)