At what age should a person stop working?

At what age should a person retire? The retirement age in most private companies was 55 years (in some it was 57) at the turn of the century (a friend of mine retired at the age of 57 in 2001). Nowadays a man or woman has to stop working at the age of 60 or, in some firms, 65. 

When I was in my thirties (1974-83), I would see men approaching the dreaded age of 55 with trepidation. Most of them would be obese and unfit to do any real work. They would pass their last six months prior to retirement just warming their chairs. Some of the more intrepid ones would try to get a part time job after retirement (one of my uncles, a banker, worked as an accountant working in the afternoons. He died at the age of 92). Others would set up their own businesses with the money they got (gratuity or provident fund). But most of them had nothing to do except go to mosques and listen to preachers saying they should grow heavy beards if they want to enter Paradise. Most, of course, would die within five to ten years after retirement.

So it's refreshing to see men in their seventies (like Biden and Sanders) trying to get elected as presidents of the U.S. Even though life expectancy in Pakistan is about 65, you do see many 70-80 year old geezers (like myself) still active. I suppose this is due to modern health facilities, which keep a person healthy enough to cope with diabetes and other diseases. About half of the people I knew well in school and college have passed away, some of them many years ago. But the rest are still alive, even though most of them don't work anymore.