If age makes Biden incapable of doing the job, then okay. But if you're saying age is a barrier to being elected, then you're saying that any factor can be considered, like being gay or being a woman, for example. You obviously don't think that being gay or being a woman should be considered, or you wouldn't have put Harris or Buttigieg forward as alternatives.

And its clear that Biden's age (i.e. experience), is a major factor in the success of his presidency. So I respectfully disagree with your assessment.