I reckon this would be self-correcting. If the average person could reach retirement in such a small fraction of their lifespan, then the vast majority of the population at any given time would be non-productive retirees. The economy would slow until your interest was zero and you'd be forced back to work. Eventually an equilibrium would be reached, wherein the average Joe could look forward to a rewarding and fulfilling career of, say, 450 years or so.