Most martial arts expect a student to reach a 3rd dan standard before training to become an Instructor.
This is a good guideline for tai chi chuan also.
Typically a Tai Chi Chuan Instructor has at least 10 years experience
and is ideally a lineage disciple.
They have a serious commitment to home practice and clear evidence of ability in all
8 areas of skill.
An Instructor should be able to
posture of the Yang Cheng Fu form (or equivalent) in a wide variety of ways.