Looks like he is more than just a “normal good math student”, as he will be two years ahead in math by high school graduation (though it looks he was three years ahead in 10th grade but the high school slow-paces math, even for really good-in-math students).
What it probably means that if he wants to major in math, he will probably want to find graduate level math course offerings and enough research activity that he can do graduate level research as an undergraduate at the school he attends. Math department faculty rosters and course catalogs on college web sites can help.
Good offerings in applied areas (e.g. statistics, economics, computer science, operations research) may be desirable to add a little variety, or if he wants to prepare for other post-graduation options besides PhD study in math.