I think term limits for Congress, Senate and supreme court would be a better solution. You can be Bernie and be old and lucid and not totally stuck the past but if you've been in office for 50 years GTFO and let someone else try.
It would need to be a fairly large limit. Places that have have short term limits have ended up seeing worse legislators with more corruption. It's easier for the rich and retired to run often, after all.
When Ralph Nader was asked about this, he said "12 years", since, after that amount of time, most of them have either "worn out or sold out". It isn't a terribly long term, but it is 3x longer than a presidential term.
I don't typically agree with Nader, but 12 does sound fairly reasonable. It's two consecutive Senate terms or six consecutive House terms, which are plenty.
I'd make an exception with the supreme court, where a term is 18 years instead. With 9 justices, that comes out to a new justice every 2 years if you spread it out equally. They'd also have a strict term limit of 1 term, you can't serve as a justice more than once.
We can do both but the existence of one old lucid person doesn't mean we shouldn't be avoiding 65 year olds holding onto power. They're demonstrably worse at politics: you can tell because a reality tv boomer bumble is dividing our country and we're in a frequently hot civil war with an actual insurgency targeting power plants.
All of these equivocators about the issue seem to fail to understand what has actually happened with mass boomer dementia. That needs to change. Learn the party line: 65 or over, no more governing.