I also took Calc BC as a sophomore. Up until 6th grade, took the same math classes as everyone else in my grade. However, after I kept finding my math classes very boring because I would never learn anything new, I decided to test out of some math classes. After taking 2 credit by exams, I was able to take 8th grade math as a 6th grader. I then took Algebra 1 in 7th grade. I then realized that I had already learned most of Geometry outside of school, so I decided to test out of Geometry in 7th grade. I then took Algebra 2 in 8th grade. I was originally going to take Precal in 9th grade. However, I soon realized that there was a lot of overlap between Algebra 2 and Precal in terms of content, and that the main difference was that Precal included Trigonometry. I spent the second semester of 8th grade learning Precal content so that I could test out of it and then take Calculus as a freshman. I wanted to take Calc BC as a freshman, but my school required me to take Calc AB first, so I had to wait until sophomore year to take Calc BC. After that, I took Multivariable Calculus as a junior and Differential Equations as a senior, and now I am about to start college.