Billionaire Carlos Slim, age 73, says workers—those in developed economies, anyway—are at their prime in their 60s.
"When you have an industrial economy like in the past where people ... do a lot of physical work and people live less years, it's OK to retire at 65," Slim told CNBC. "When you have a society of knowledge and experience and information, at this age is where you are at your best. It's [foolish] to retire at this age. And you don't have the physical work, and you have the intellectual work and you are in your best in your 60s."
(Read More: Average Senior Is Living on 57 Percent of Full Pay)
The comment came up in a discussion about what to do to fix the European economy. Many economists and politicians have said retirement ages around the world need to rise because people are living longer and the benefits promised to retirees are unsustainable. However, Slim said, even beyond that, workers are better in their 60s than when they're younger.