The one solution is to end the back story bad 'so anyway, he's learning how to walk again after... That.' or 'crawled into a bottle afterwards, and you'll have a hell of a time fishing her out. In the meantime, she can still manage a cantrip from time to time. Most days.' Especially if you're going for a 'last job' or 'old gunslinger' vibe.

Works really well if your early build is super specialized, and, like 'they still remember how to do that part just on reflex'

Or just start the campaign at a higher level.

Ohhh, that's a good one. I'm stealing that!

Hence the number one rule: cool stuff should be done in the game, not your backstory.

I prefer Fate, where the rules practically require having cool stuff in each character's back story.