[untog]

There's another element in there - that older candidates simply have more history to contend with. That's not always a bad thing, like Bernie Sanders' presence in the anti-racism protests of the 60s. But it can be a bad thing, like Bernie Sanders having taken a trip to the USSR in 1988 (I won't disagree with anyone who says that isn't actually a thing to care about, but people do). Biden in particular is going to come up against a lot of issues for his previous zero-tolerance crime advocacy, and for the treatment of Anita Hill during the Clarence Thomas confirmation hearings.

Younger candidates simply don't have to contend with that reckoning. But they have a lot less experience. You could make the case that experience should be good for a candidate, but that it doesn't always work out that way.