Yes I can't see how that would be sustainable in the current economic state. Perhaps the retirement age would have to increase in line with the years added to the average lifespan.
Obviously the economic/social impact would be enormous and would require many difficult decisions but difficult != impossible. These are challenges that would surely be worth overcoming?
The whole reason that we have Social Security and Medicare is that as people get old, they lose the physical and often mental capabilities needed for work. Fix that and there's no need for permanent retirement, and medical expenses fall drastically.
Obviously the economic/social impact would be enormous and would require many difficult decisions but difficult != impossible. These are challenges that would surely be worth overcoming?