This is the way. Age is just a number. Until it isn't. Biden could probably, with all the team around him, finish out a second term. But the demands of looking sharp in situations like debates (which are not really great tests for doing the job, but it's part of the performative bullshit clown show we put on for the low information voters and they will decide elections in our stupid system) was going to sink any chance of him winning this fall.
And Bernie apparently has all his faculties and has the EQ to understand the plight of many Americans. Counting someone like Bernie out only because of the number of times they went around the sun? Impossibly stupid. And, as I keep emphasizing, more and more likely to become entirely irrelevant as things like age reversal come online.