It’s not about being too old per se, it’s about being too unhealthy. A person can be 80 and still mentally fit, just like a person could be 60 and totally frazzled.
The only reason age comes up is because there’s a correlation between age and cognitive decline.
Don't listen to these people who call you some sort of Russian bot. They want to shut their eyes and pretend like nothing is wrong, while we are on the verge of an authoritarian Trump presidency.
Edit: for the record, if Joe Biden is the nominee, you still gotta vote for him. I'm not saying otherwise