Well, with all the quests completed and all troops killed, that should amount to lvl 51-52. If you took learning early and used some other XP boosting items, you can get to about 57. In my last game as a mage I actually found 2 +10% XP gloves, but the second one was really late in the game, and it spawned after I killed K'Tahu, so... 57 is tops in my opinion. If you can get 2 necro gloves, the shark tooth (guaranteed) and the marshal's memoirs, that's 30% xp per battle. Learning gives another 20%, so that's 50% per battle. That should push you into the 58th, probably 59th level, but getting all those in the beginning of the game is highly unlikely.
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