> I do think there’s a risk of societal stagnation if we all stick around forever. But, maybe we can make a deal—if we all end up immortal, we can make a threshold, maybe even as young as 80 or something, and have people retire and stop voting at that point. Let society stay vivacious, sure. Give us an end point for our toils, definitely, and a deadline for our projects.

Your idea obviously doesn't work. You're basically advocating for something like Chronic lymphocyte leukemia at the society level (https://en.wikipedia.org/wiki/Chronic_lymphocytic_leukemia).