Only way to do this will be with a Convention of States.
https://conventionofstates.com
If the Senators were appointed by the States like originally were instead of elected by the masses two things would happen; 1. Big money would be out of the election - they would have to spread around to 435 congressmen instead of a handful of Senators each election cycle. and 2. Senators would vote in the interest of their State because they could get recalled or not get reappointed when their term is up.
You'd need to amend the constitution again still. 17th moved senatorial elections to direct elections from appointment by state legislatures.
IMHO I think we SHOULD be directly voting on those running at least the executive and legislative branches. So I am not remotely supportive of overturning that one.
That said, I am firmly supportive of term AND age limits.
IMHO, for the later, set it to the social security full retirement age probably. As we live longer and in better health, you can serve longer.
But IMHO doesn't matter your party, some late 70 something, let alone 80 something year old should not be running the government. If the maximum age to start a term in office was 67, that would probably do the country a world of good. Hard to be as connected with real current issues or what the majority of Americans (even of your own party) actually care about when you are 1-3 generations older than the majority of your constituents.
I would argue that to a degree a part time elected official isn't a great idea. Or at least one who has very limited experience. Hard to understand how your government really functions with no experience. That said, I think for the house it should be no more than 4 terms, senate 2 and President of course 2. If you really went through all of those offices, that is 30 years in government. That is a full career. Spend your 4 terms and can't get elected to the senate. I guess you are out. Or try again another time to the senate or whatever.