Guy fails high school math, but yes, have him ditch school, drive his mom's car to a university and audit college calculus.
I failed (got an F grade) in high school math for two years, because of bad teachers and chaotic classrooms. Eventually I just stopped going to class, guaranteeing a failing grade regardless of whether I understood math. At the same time I got through two years of math classes (trig and calculus) at a nearby university. I did that on advice from my high school counselor, who then gave me math credit because she understood the difference between high school grades and learning.
Statistics and probability came later, you're right.
Basic understanding of statistics informs us that aggregate results do not predict individual outcomes. The aggregate poor math performance of American high school students does not predict what any individual may achieve (or fail to achieve). The overall poor math grades and test scores among American high school students could have any number of causes. Overwhelmed or disengaged teachers and a one size fits all curriculum probably have something to do with it.
My comment was intended to get the original poster to think about taking control over their education rather than expecting school to do that for them. If high school math classes aren't working then look into alternatives. The OP already indicated they care about learning math, but aren't necessarily motivated to achieve good grades to get into one of the "best universities."
Actually, that's precisely what it does.
You can learn on your own from books and online resources, find a mentor if you’re lucky. You can simply stop attending school and homeschool if your parents will cooperate. High school students generally can take classes at universities and community colleges. You can find all kinds of resources once you manage to free yourself from compulsory school attendance.
A high school diploma has some value in the job market, but you can get a diploma from community college or by examination in some states, you can look into that.