Who's too old to run for president?

I think in the future, Biden's actually quite tardy realization that he is simply too old and (quite normally) infirm to run for re-election as president, will be regarded as self-evident. Those who said he should never have decided to run in 24 in the first place will be thought to have been rather obviously right. Of course, since the Orange Menace, in addition to his utterly disqualifying behavior and lack of relevant skills or integrity, will be older than Biden is now well before the end of a term if, heaven forfend, he wins election, it should be pretty obvious that it is he, not the Democratic candidate, who is too old to run for president. This fact is sitting there and will not go away, and it may, just may, be what defeats him. Trump's unquestionable and severe narcissistic personality disorder and incipient dementia will obviously not help him either, but even if you somehow give him a pass on all his profoundly stupid and terrifying policy positions, you have to recognize that this horrible man, based merely on his mental health and cognitive impairment, not to mention poor physical health, has no business being a candidate for any responsible office, much less the presidency.