Just like you I do not think that there should be any set time for someone to retire because someone that is at 60 and still strong might be able to carry on their work even quite into at still strong so I will say it is that age where you feel that you do not have the required strength again to carry out your job that you should retire.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.