For my view point I think the entrepreneur should retire when him physical fitness is not longer there anymore, when the person does not have the power to do what is needed to him to do in the business, then him or she can retire from the business.I think it depends on the mental and physical well-being of the entrepreneur if you are still mentally or physically Fit at the age of 70 you can still run your day to day business if not then I think no matter your age you should retire.