For another data point, I took it in 7th grade too, that was only--oh god 2003 was nearly 20 years ago. Anyway, it was considered one year early for my public school district in Utah. Me and a few others in my 6th grade class who had good math grades were offered the chance to sign up for it early if we were able to pass a test administered by the junior high. I don't remember what the test had on it, I do remember asking people around me (at least parents and GED-holding brother) "What is algebra anyway?" and not receiving an answer, but somehow I passed. One friend also passed but didn't sign up, instead doing "pre-algebra" like most kids, which made me sad. (I'd guess the test had things like "if x + 3 = 10, multiple choice what is x?" as sort of a sink-or-swim filter, or maybe just some more advanced examples of whatever the 6th grade curriculum entailed.)