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."

Apologies for double posting - issue with my ipad bluetooth keyboard