I'd say the term "genius" in this context is getting used as an adjective, which it is not - the adjective type is "ingenious". "Boy genius" is idiomatically preferable, as indicated elsewhere. , like "greatest", or "greatest", so just as you would probably use it being an adjective to point https://franciscoffcki.theideasblog.com/37054622/the-smart-trick-of-where-to-find-secret-crows-in-the-genius-crow-that-nobody-is-discussing