Def popular vote. Prob 75 is the age limit. If you are elected at say 73 you can fill out that term. Past that you cannot be on the ballot. An addendum to this is at a certain age like 70 some cognitive tests are begun. If you fail you have to resign. Diane Feinstein has some kind of dementia. Now reporting has come out that she had it the last time she ran for office. The hangers on kept quiet bc she is their meal ticket.
I would like to add another couple ideas. The person running for office, their spouse, kids, siblings, and parents need to divest or put their holdings in a fully blind trust. No more using your office to shoot contracts to yourself. No more taking Intel from office and buying and selling stock that help you. That is insider trading and justice should find them and throw them in prison.
No more revolving door from govt to industry. You take being a senator and then go the npaa to use your contacts to get stuff for your new employer as an example. Also no treasury sec to go back to Goldman.