As time goes by, we’ll become older. It means that our brain and our body will not work as good as when we’re younger. For example, maybe we’ll forget something easily and harder to concentrate. If that happens, there’s a lot of chance we can’t finish our work well. That’s why for those who work to other people, it is appropriate if one day he will quit from his job in range of certain age. But for those who are entrepreneurs, they could work as long as they want. Even if he stops working, usually it’s because of his healthy is not well anymore.
In fact, for the boss of the office, it’s not an easy thing to retire his employer. The boss will look out how the employer’s willing to work and productivity. If the employer’s age is old enough but still has high productivity and willing, the boss will think more than once to retire him. On the other hand, the boss will easily retire his employer who has low productivity and willingness even though the employer is still young.
Even if the productive employer is retired, maybe it’s because the boss see the potency of the newcomer. Or maybe the retired employer is someone who has the lowest productivity among other employers who has high productivity. The healthy of the employer is also a reason to be retired.
Over all, there is no certain age for someone to retire. “It depends whether you're looking at the issue from the point of view of the employee. (Peter Calver, http://comment.ft.com/2/OpenTopic?q=Y&a=tpc&s=646099322&f=386092324&m=2770964011).” It also depends to the employer’s quality itself.