I think that’s their point: That maybe, as long as a candidate is mentally fit, then voters ought to be able to continue voting for them if they feel like the candidate is still worth voting for.

Honestly, if there was some kind of magical bullet to simply ban candidates who are mentally unfit (i.e. losing their marbles) from holding office that couldn’t be exploited, I think a lot of people would find that preferable to an age limit.

That doesn’t address issues like politicians who are too technologically illiterate to do things like open PDF files, though.