You got me there. The questionable aspects of 18th-century political sociology fundamentally *refute* the moral arguments in favor of democracy, in the same way diagonalization arguments refute theorems in computability theory. It's ironclad math.

Democracy can overrule those, there's a defined process for it.

IMO they should, there's no need for these laws to be cast in stone and never change.

Yes

Honestly I the existing and proposed age limits (e.g. that you can't serve as President over 80) are addressing symptoms of a deeper problem. If your country's population wants to elect a senile 90 year-old or dumb 18 year-old or Russian traitor, your democracy is deeply flawed. A law preventing the people from doing so won't save them, as they can just elect someone else incompetent. If voters know what they're doing we shouldn't need requirements for people to run for office.

Presidential term limits in the US were only instituted as a reaction against a president (FDR) who was very popular among voters, but far less popular with the Chamber of Commerce.

The Chamber of Commerce tried earlier to specifically institute a term limit for FDR, but it didn't work out: https://en.wikipedia.org/wiki/Business_Plot