I wouldn’t take the subject tests in any old subject, make sure they make sense with potential future plans like Math2 and physics or chem for your son. My kids are also grade advanced in math and they did need to review Geometry a bit before taking the Math2 because it was so long ago and not skills that are built on or used in other subjects like basic algebra. We are lucky that our school offers a dual enrollment option for Multi Var and Matrix Algebra through a 4 year college so MIT has accepted the transfer credits from previous students but they rarely accept them from 2 year colleges. The Physics SAT2 does not sync up with the AP curriculum. There were 3 units that were not covered in AP Physics 1 on the SAT2 and there may be 1 more unit for kids from other schools as our school did one extra unit after the AP test. For a kid who is gifted in math and physics it’s an easy few hours of self study though. My son took AP Stats as an elective and thought it was one of the least interesting and challenging AP classes. No homework and he easily got a 5 without studying. Not going to impress schools who know what real upper level math looks like. If you don’t have any resources for more math I would make sure he does everything he can to self study and be prepared to find ways to work that into his applications.