OP characters who seem to be permanently level 1, just remind me of the level grind of the old games like Ragnarok Online. It's possible to hit level 100, then reset to level 1 and evolve into another higher form of your class, but the exp requirement is...
My headcanon in this is the display can only display double-digits. If his previous life's level was capped at 100, then his actual level now is something like 101.