I don't understand all the talk about Biden being old and frail. He hasn't even reached 80 yet, can still walk and talk properly and I'd say the talk about him being senile due to the way he talks is quite exaggerated. Consider also that there's a lot of deepfakes of him out there and that he stutters. I've watched a couple of his recent speeches and he looks great, sounds okay and doesn't need papers. We'll know right away if something big actually changes in his behavior.
If you compare him to other current leaders such as Uganda's President Yoweri Museveni, Cambodia's Hun Sen or the Czech Republic's Milos Zeman you see that things could be much worse. 77-year old Museveni couldn't take his eyes off his UN speech paper, 69-year old Sen sounds increasingly frail and Zeman is a frequently hospitalised 77-year old alcoholic in a wheelchair.
Dole's age was a consern for many around the 1996 elections and he wasn't even in a bad shape back then. He had just survived a cancer and already at that point was using a ton of meds. 25 years later he's still somehow going.
Pope Ben was 78 when he was elected in 2005, had suffered a stroke in 1991 and a mild one in the same or previous year he was elected and had troubles sleeping and heart problems, many thought his reign and remaining life would be very short. Pope for nearly eight years and now retired for eight years.
I think he'll live to his mid-late eighties unless something sudden, (a fast health decline) heart attack, stroke or cancer happens.