Colleges have replaced high schools, since high schools stopped letting people fail out. That means modern colleges teach at about what used to be a grade 9, maybe 10 level, for their first year, to "catch up" all the quota students and bonus paycheck students that shouldn't have gotten in in the first place but did because high schools just arbitrarily give good marks.
So it's likely a homeschool thing, that he actually has a grade 9's knowledge in grade 9, instead of in grade 13.
Colleges have replaced high schools, since high schools stopped letting people fail out. That means modern colleges teach at about what used to be a grade 9, maybe 10 level, for their first year, to "catch up" all the quota students and bonus paycheck students that shouldn't have gotten in in the first place but did because high schools just arbitrarily give good marks.
So it's likely a homeschool thing, that he actually has a grade 9's knowledge in grade 9, instead of in grade 13.