Dude, come on. What happened to you?
The oldest person to assume the presidency was Donald Trump, at the age of 70 years, 220 days, on Inauguration Day. Biden will be 78 on his Inauguration Day.
I'm not saying he will go senile, i'm saying it's a possibility. He's not the same man he was during the Obama admin. Reagan suffered from dementia while serving as POTUS, and he LEFT the White House at age 78.
It's also a possibility with Trump. Trump is mentally unstable even without a brain-eroding disease. That's absolutely frightening.