It does seem to me that there should be a level 30 or 33 limit too.
But players should also be warmed in level up screens about the next level cap before they reached it something like; 'you reached level 15, and can play at any level between level 10 and level 20, after level 20 you will be able to play at level 20 to level 30.'
It will serve to protect newbies from the pros, even though 20-30's will be able to farm with Lucifer torso for a while, they will then become the pray at level 30 - thats the cycle of life in Mech's.
Having been a farmer at 23 for a while, they should be sufficiently switched on to get the cash for a level 30+ (33) build before hitting the cap - if not, then they learn the hard way
It will also importantly serve to force a viable population at level 33 (ish).
While I agree with TheS about number of battles, it would be hard to enforce without a level cap system, we could still have level 23 build domination of population, even though the new players would be protected, it wouldnt force the numbers playing at 30+ up. I believe forcing the number of players using higher builds for PvP upwards away from the 23 build is a good thing.