Doogle, yes the legality is true, at 70 your China motorcycling days are supposed to be over and new licenses won't be issued after 60. However these laws change all the time. When a sizeable number of people get to 60 and want to keep riding critical mass will change the age limit upwards, this just happened, in fact with cars. You could try riding on an international license and claim ignorance or try finding some organisation that could help you get a temporary license. A temporary car license would be better than nothing.

Also remember that, for sure the bigger the city, the more rules are enforced. I wouldn't want to ride in Shanghai in daylight hours without being 100% legal. However being in the countryside having registration, insurance and any sort of license from any country would be a miracle for most of the locals.

To sum up I would say; yes you likely can't be legal. If your dream is to ride in cities or between them, then I also would say no, it might be a bad idea. However if you are happy to ride in rural areas and villages you would probably be OK if you had a legal insured and registered bike, but I'm not condoning you take any risk, just that the risk is to my knowledge fairly low.