I can actually agree with you from experience. I was homeschooled from age 13, but my parents didn’t know enough math to home school me in it, so my mother got me into a dual-enrollment program with a community college for math and CS. Overall I did ok, but calculus really threw me for a loop, and I ended up scraping through calc I & II with C’s. I often wonder if I had taken those classes when I was 20 rather than 15 if I would have done any better. My own son took the test (at his math teachers urging) to get into high school algebra while he was still in middle school. He didn’t pass the test, so he had to take plain-old middle-school algebra, and he was actually a little bummed out about it. I told him that when you’re 30, the only thing that really matters (if anything) is where you went to school, which depends a LOT on your test scores… not how old you were when you took the tests. He knew some of the kids who “made the cut”, and they struggled with high school algebra, got B’s and C’s, and one actually dropped out of high school last year while my son is still a straight A student.