No, that is not normal. Apparently you ran into a bugy experience bomb
, that gave you much more than the usual experience bonus. I played with Resurrect a bit (re-killing monsters for more experience) and delayed the wishing well and imp council member quests in order to make the best use of the level-ups, and finished the game on level 53 (the wastelands were a cakewalk). The usual end level range is from the mid forties to very low fifties (and that is including the 5 level bonus you get entering the wastelands).
Experience is based on your level; the lower your level with respect to an opponent the more experience you will get (and if your level is much higher you stop getting experience), while with quests, the higher your level the more experience you get.
I imagine a high level would speed things up, as you would blow through mobs much faster and would not need to worry as much about strategy with difficult opponents.
You may be able to use iZakaroN's SaveEditor
(or from Kiya's site
, with description) to change your experience points (not sure if that will drop your level, though), or at least lower your stats to what they should be to make the game more challenging. If the level does not drop after you reload the save and complete a quest or something to update your experience points, you can change it manually;
Some more hex offsets...