You can currently continue to fly with your current employer to 60, and even pass 60 on a case by case extension basis. But when a local Chinese pilot switches, job, Airline B has to pay Airline A a huge sum of money (in the tune of $700k USD, I last heard), not unlike a footballer transfer fee, hence the low 50-yr old range hiring norm. In China, some of the rules don't even make sense to local Chinese. Case in point being that a certain percentage of applicants must fail a test, any test (medical included). You can see that the system and the medical exam are your biggest problems rather than age.