I agree Bernie is pretty sharp. But Bernie is, in many ways, a unique case. We have a minimum, 35, we should have a max, 65.
That gives presidential candidates a good opportunity to gain life and work experience. It also keeps the ideas fresh and out of life long political careers. Anyone over 65 can be hired as a consultant, or one of many other positions. States obviously set their own rules for local governing, but I think it should apply locally too.
That would be rather ridiculous. Age is just a number (especially as we may be on the precipice of age slowing/age reversal). I'd be for reliable mental acuity type of screening.