About ten years ago I compiled a bunch of demographic data and compiled my own conditional probability tables, i.e. given you are X years old, what is your probability of surviving for another 1/5/10 years:
My numbers are somewhere between what @WalterBishop and @Riemann cited. Given that Joe Biden is 81 right now, I show he’s got a 56% chance of surviving to 86 (i.e. completing a second term as President), and a 47% chance of surviving to 87, i.e. his remaining life expectancy (without considering any other info) is somewhere between five and six years.
If you add in the fact that he’s got access to great health care, is not socially isolated, and seems to get at least a bit of exercise, I think he’s probably got pretty good odds of making it into his 90s. That said, he’s already moving and speaking more slowly than he did when he was campaigning in 2020; I’d rather see him in office than Trump for the next four years, but I am concerned about what kind of condition he’ll be in as he approaches the end of a second term.