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<p>That is already a year advanced from the typical sequence starting at algebra 1 in 9th grade and finishing at precalculus in 12th grade. I.e. he will take calculus in 12th grade, which is more than sufficient for admission to and preparation for any college in the US, assuming good quality high school courses.</p>
<p>As far as the economics major goes, economics in preparation for PhD study in economics requires considerable advanced math and statistics, including college junior level math major courses like real analysis. But the more common type of economics majors typically need just a year of college frosh level calculus and a semester of statistics. Assuming good quality high school math courses, taking calculus in 12th grade is more than sufficient for either path, though.</p>