You don't need a constraint based on age. You need a thorough vetting process to keep out criminals.

I'm not even sure Biden's dementia is real. It could be an act to make the Democrats look like idiots, and justify not following their full agenda or it could be an act to try to avoid being put on trial. If it is the later apparently it worked since he is to senile to charge for the document theft he committed back when he knew exactly what he was doing.