My grandfather kept all his marbles until he died at 101. Last time I saw him, about a year before that, he was still whipping me at chess. I was a strong player at the time.

I'm 70 now, still doing software full-time in a highly technical organization, and I can still write tight, clean code more quickly than most. I mainly do it for proofs of concept, such as when the dev team are being risk-averse and say something can't be done that I know actually can be. I have less physical stamina than I did in my 20s, but my mental acuity's just fine so far.

Dementia odds do go up, but are still not that high in one's 70s, and are even lower if, like me, you have good cardio fitness and eat a healthy diet. That lessens the chances of vascular dementia. Harder to say if it helps with Alzheimers, since there's a significant hereditary component to that, and research isn't clear on how big that might be.

So try being fact-based when you're proposing political solutions. Every day, we're seeing what happens when politics is being driven by prejudice rather than truth. We don't need more of that.

I'm aiming this upthread, not so much at the post I'm directly replying to, which I agree with.

I don't think there should be an age limit but I don't think it's unreasonable beyond a certain age to require people to prove cognitive function. There are many countries in the world where they do that for driving tests which seems perfectly reasonable.