W/o commenting on gerontocracies, this would mean that folks Biden's age wouldn't suffer as they do now from the deleterious effects of ageing.
Put otherwise, Biden wouldn't be old at 81 if we completely understood the molecular biology of ageing. Unfortunately, we don't.
Tho these people might not update their politics (I don’t have a sense that Biden ever did) and so while they may not suffer mental decline, we could find ourselves deprived of new thinking.
We could always regulate that politically. An age limit for public service, though I guess that doesn’t cover most powerful people. Overall I hope that if we had figured out aging we’d be smart enough to deal with the consequences well but who knows.
Hard to get the gerontocracy to vote against a gerontocracy. We can't even get proportional representation voting systems (at least not in the USA). Quite unfortunately, our system is built to protect the power of those who created it; it is not built to be smart.