My parents are past 65, and my mom is still easily able to spend a full day taking care of our 1 year old, and my dad spent the last few weeks cutting down trees on his property. (They spent the first 40 years of their life in Bangladesh, so your point about healthcare probably isn’t correct either.) Only a small fraction of people work hard physical labor that someone 65-75 could not do. And of course some people won’t be able to do even a normal service job, but you don’t need everyone to keep working, just most people.

As to the societal failure—its a self-engineered one. Maybe some day we’ll have robots doing all the work, but we’re not there yet. Singapore’s GDP per capita is $90,000 per working person. Enough where you can have a functional retirement system, but not so much that doubling the number of retirees per worker won’t seriously be painful.