I don't really care much about her age. Sure, she's old and should probably retire soon, but she's been an effective representative and shows no signs of mental decline. I'm fine with her having one more term if she's capable, and if she has to retire before completing it, a Democratic governor will appoint her replacement.
We've all had fairly recent object lessons that youth isn't everything anyway, with the combination clown-and-shit-show on the right. I'd much rather have Pelosi stay than, say, George Santos or Lauren Boebert, and they're both half her age.
The problem with your scenario is that she is in a democratic strong hold. A Boebert or Santos cannot possibly win but a younger, more progressive and truly representative candidate could win. She's preventing that progress by holding onto power till they can't weekend at Nancy's her corpse anymore.
The problem with your scenario is that you have another young person that is really enthusiastic about changing everything but doesn't know how anything works and can't get anything done. You may love people like AOC, but what legislation has she actually gotten passed?
Pelosi knows how the system works and knows how to actually get legislation passed. Sure if you're young it feels like compromise is selling out, but it's at least something. Saying a lot while doing nothing gets internet likes, but it's not actually progress. It's just talk and political theater.
If the Democrats win the House the new Speaker will benefit from the many years of experience that Pelosi has. That is if you want legislation that will actually improve things instead of just talk.