Doctors in China are basically three or two and a half years old. But this is not the case. Most doctors are studying on the job, because they often delay graduation for four or five years because they can't finish their thesis. In addition, if there is no result during the doctoral study or the tutor refuses to graduate, it will be delayed in the future. It is ideal to graduate in three years. Most schools have to publish several articles on CSSCI before they can graduate. I hope it helps you.