No, because that's literally agism.

I understand that it's tempting to think that old age necessarily means degraded mental faculties, but there is no scientific link between the two. There are people who develop Alzheimer's in their 30s, and others who remain lucid into their 100s. Tomorrow there could be a scientific breakthrough that doubles the average lifespan of every human on earth, and we'd be sitting here with an irrelevant age limit on the books like simpletons. The abilities of the person are what matters, the number itself is a red herring (in the same way that the color of their skin should not be used to infer anything).

If the issue is term length, then put a term limit on the position. Otherwise, democracy means the people will elect the wrong people sometimes. We're in a unique situation where the baby boomer generation has more voting power than the rest of the population, but this issue will resolve itself.

Edit: the AARP's position on the matter