He’s certainly very strong. How he does on this year’s Olympiad paper (i.e., consistency of performance) will also reveal where he’s at and which curriculum and/or enrichment activities might suit him.
FYI, in my D22’s high school class, the strongest math student won “book awards” with some regularity and ended up with 1 HYPSM offer but decided to pursue STEM (but not math) at Oxbridge; what impressed me most was that she seemed to be achieving these results with relative ease.