As a general rule, any adventurer that's higher than 10th level is already a figure of renown, a household name. Anyone higher than 15th level is a figure of legend, somebody whose deeds bards will sing of for centuries, and anybody 20th level or higher is basically so powerful they start to consort with deities and planar figures on a personal basis.
Really? That's interesting. In my assassin playthrough of BG2, at the end of ToB my rogue was L41 and other single-class party members were all around L30. lulz.
But then in ToB you do talk to Solars and fight top-rank demons every few hours. You run into a squad of balors and you'd be like so what should we have for dinner.
This sounds like one of those "rules" that are better off mostly ignored. I mean, as long as it's exciting and the balancing is alright, who cares. Well, I guess the hardcore PnP folk care.