I don’t think it is too early, but I would have him take both the ACT and SAT to see if he likes one better. My Ds had to take both PSAT and Plan ACT in fall of 10th. Over summer my D21 studied for the ACT, took it in September. She will have to take it again in February because our state requires it. Now she knows what she needs to work on before February.
I can’t imagine waiting until August/Sept. of Senior year. My D18 was done applying by August. Plus it is really hard to make a realistic school list without a test result. I’d rather spend that summer visiting realistic school choices and applying.