Working visa for an English teacher, 61 years old.

I am a citizen of the United Kingdom. I have been teaching in Japan for 29 years. I have been offered a very good teaching job in China but I am 61 years old. I know I cannot receive a working visa at my age. I have been told that I can get a Business Visa. If it is possible to get this visa, would it involve me having to exit and reenter China every two months? How long would I be able to keep on renewing this visa? I would be very much obliged if you could help me with these questions. Thank you for your time, Paul Curtis.