The question becomes at what age is there an assurance that mental capacity is not capable of doing the job? There is no age within any president in the past that has a truncated data point where all on one side are capable and all on one side are incapable. Instead, there is a distribution that when averaged in time slots is normalized, as are all averages, even with a single tailed distribution which would be the interest for a metric of age on mental capacity. The math for an age restriction for a single candidate is much different than a group of voters.
With a single candidate it is possible to see the mental deficiencies, as many of us saw in Biden. Those deficiencies were decades earlier, and something Obama knew. Still, others will choose to not see those, have other areas of interest, or not care.
When establishing an age metric for voters, the math is currently impossible to study all the voters and so an average or single data point makes more sense…knowing that you don’t know the voter’s ability to vote intelligently for each, losing some population from the mean on both sides. The goal at that point should be at what age does a voter on average have enough understanding that evolutionary growth of knowledge through life experiences, study, and reflection, be apparent to make an intelligent vote and a single data point makes “more” sense until a better evaluation if possible is in place.
Similar is term limits…we all have the ability to set those terms without an external number and that too is a reflection on the voter…