Fitness coaches don't require academic qualifications, but junior college is certainly ok, but they still need some knowledge and expressive ability, because coaches sometimes rely on letting students understand your ideas, which requires rich knowledge and the basic quality of a culture.
If you want to be an excellent fitness instructor, you don't need to get any certificates. First of all, you should have rich fitness experience and systematic study, and you should understand the actions and knowledge you want to give to the students. At present, general gymnasiums require fitness instructors to hold coaching certificates. Generally speaking, at least the national second-level coach, and that one needs to pass the exam, and then take the first-level and special-level exams.
Fitness instructors are popular not only when they are young, but also when they are old. The coaches in our gym are over 60, and they are still excellent. Yang Jingmin, coach of the national bodybuilding team, has trained many national champions. Yang Xinmin, a senior champion, is also an excellent fitness coach. So the fitness instructor is very old. It doesn't matter.
Finally, I suggest you find a famous coach to study and practice systematically. Take part in the competition and get some excellent results. In this way, you have the capital to be a coach in the gym and find more students. This is my advice to you. You are still too young, and of course you lack experience. You still need to learn.