Being a coach in Korea is very strict and requires a lot of certificates.
So it depends on what you are after.
If the average person practices every day, he can almost get a black one a year.
I don't know your level. I don't know.
People are different.
You are not old enough to work hard.
Taekwondo coach is not only technical, but also spiritual.
Responsible, polite and serious attitude, hard work and desire.
If you don't give up, you will get what you want.