Changzhou Naji Taekwondo Gymnasium is the best.

Changzhou Glass Road Pavilion and Jinlu Pavilion (Changzhou) branch are both good. It is not difficult to take the black belt test. It usually takes about a year to a year and a half. However, if you want to go to the ninth grade, you must be over 53 to qualify. You are now 13 years old, and it is not difficult to study. You can study at any time. I wish you success.