There are two answers here - one short and one longer (but probably more accurate).
This is the short answer. Most students attending a regular set of twice-weekly classes year-round should be able to complete their black belt requirements in less than four years. This can vary from do-jang to do-jang, but this is the average time to earn a black belt at Red Phoenix Tae Kwon Do.
Some see the path to a black belt as a sequence of ten promotion tests or belt tests, each with requisite technical skills, poomse and sparring requirements. This is true, and in addition, students have increased levels of responsibility with each level. This focuses on showing leadership in the class and outside of class. This focus matches with rising expectations for thoughtfulness about Tae Kwon Do, its philosophy, and contribution to personal goals.
This is the long answer. We've had some students who reached their red belt or black stripe and then paused as school or work required their focus for a while. Then, they returned with renewed commitment to the martial art. For them, this might add another year to their training. So, this long answer is that the journey to a black belt is a personal one that fits with an individual’s timeline and priorities.
We’ve had 8 year olds achieve their first poom level (for youth, a first poom is the equivalent of a first Dan), and we’ve also had 70-year-old retirees earn their black belt. The timing is up to each student.
When you attend a class, check in with your classmates and learn more about their unique Tae Kwon Do journey.