They are panicked.
They aren’t panicked about Biden’s age, though, they’re panicked about a potential Trump presidency, and their time would be better spent explaining why that prospect is worthy of panic.
Yes, at the core, the panic is "I'm worried Joe Biden will lose to Donald Trump."
But a lot of people clearly have strong feelings about it, and about what to do or not do in response. Expressing and arguing is probably a better way to move on from that than trying to avoid it indefinitely.