In his first presidential primary in 1988, Biden was the front runner despite his youth because he was wildly regarded as one of the best public speakers in the country and he was (at the time) charismatic.

Then he started yelling at reporters about how high his IQ was after they found out he plagiarized speeches plagiarized work in law school, and lied about his grades and class standing.

Because he got over his childhood stutter. In childhood.

What's happening now isn't a stutter. It's 100% normal for an 82 year old.

That doesn't mean an 82 year old is fit to be president, just that Biden acts how an 82 year old is expected to act. Because he's 82 years old.