I agree also - there is also something to ones capability as you mature. I BARELY got through Algebra 1 in Junior High School (9th grade). Parents got me a tutor during the summer and got B’s in Geometry the next year. I kept on taking math and getting C’s and B’s after that...all the way through Advanced Engineering Math (Laplace Transforms,etc.) I hold an EE degree.
So - I conclude about myself that I wasn’t mentally ready for Algebra the year I took it, but a couple years later when I got to Trig/Algebra 2 - I handled it okay. I didn’t excel, but I passed.
I earn Ds in algebra I and II. When I was 24, however, I started college with the goal of entering one of the doctoral level health professions. My high school grades were so poor in math that I was not accepted in the Biology program but was accepted into another ( ironically more rigorous) science an math major. I finished all the courses offered in Calculus, differential equations, numerical analysis, engineering physics, and chemistry major's general chemistry and organic chemistry.
I did outstanding well and was accepted to all of the 5 doctoral programs to which I applied. This was in the late 70s when there were more than 20 applicants for each seat available in the health profession of my choice.
I'm a mathematician in the financial industry, but my senior year of undergrad I took a grad course at UCF called "Advanced Math for Engineers." It was very fun and interesting. I especially loved Fourier Transforms.