We need max age limits. I'd say 70, anything older is incapable of making rational decisions.
I know lots of people in their 70s or older who are smart, rational, experienced, etc. I actually think older people are more valuable overall given their life experience. There really is no substitute for the kind of experience, mistakes, life-learning, etc. that comes with age. I really wish I had the experience and understanding I have to today back when I was in my 20s.
Rather an some arbitrary age limit, I think we should just have competence exams.