The problem is not, necessarily, age but failure to evolve intellectually. Experience is the richest resource our species has but for a significant subset of the population (encouraged for political purposes in America) experience is confused with mythology to support authoritarianism.
I have the same problem with both Biden and Sanders. They have been successful in the system for so long they simply want to more of what they have always done. Biden has been hit so hard because he tried to stand on what once was middle ground. That ground does not exist. He now looks like a fool.
It was always said that youth is wasted on the young. In 21st century America experience is wasted on the old. Experience assumes a functional model that continues to be relevant. When the models change experience must be reapplied or will be critically flawed.