> Well, suppose a miraculous breakthrough occurred and the life expectancy shot from, say, 75 years up to 750, pushing back the onset of debilitating age.

I wonder how this would play out economically. Most of us here could probably retire by 100 (and many by 50) and have enough accumulated wealth to live off interest. Could we have a world where that many people live off interest forever it would the extra productive years create enough inflation that it's not feasible?