I definitely think Biden does have a stutter, but I also do think his public speaking skills have declined even when he is fluent. More flat, lower energy, speaks more slowly, etc. This person could be making fun of his stutter, but it's vague enough that it could also just referring him to just being old and not a very dynamic speaker, which I do think is an issue. To be clear, I do think he has a stutter, even if he also has other signs of being older unrelated to stuttering. It can be both things at once, and drives me nuts when people think it's not at all related to stuttering. Compensating for a stutter takes a lot of work! My take is that his skill for hiding his stutter is declining, which makes it seems like it's magically appearing out of nowhere. I'm much more likely to stutter when I'm out of my element/stressed/etc.