Your instructor will assess whether or not you are fit to be a teacher.
It is not for you to decide.

What qualities does your instructor seek?
You need to be:

1. Caring
2. Reliable
3. Earnest
4. Genuine
5. Punctual
6. Motivated
7. Committed
8. Trustworthy
9. Friendly and personable
10. Interested in other people

Beyond this, you need to have actual talent.
You cannot be lazy, indifferent or emotionally unbalanced.

There are 5 levels of Tai Chi Instructor in the UK these days:

1. Health-only Tai Chi Teacher
   - 5 years experience
   - these are the majority
   
2. Tai Chi Chuan Instructor
   - equivalent of 3rd dan black belt in any martial art
   - 5 years experience
   - these people are less common
   
3. Tai Chi Expert
   - 15 years experience
   - 10,000 hours tai chi chuan practice
   - 10 years teaching experience
   - fewer to be found
   
4. Tai Chi Master
   - 25 years experience
   - 30,000 hours tai chi chuan practice
   - 20 years teaching experience
   - pretty rare
   
5. Tai Chi Grandmaster
   - extremely rare

Peter Southwood has graded Sifu Waller as being a Tai Chi Master based upon his practice quality and experience.