The Steipler as well as the Chazon Ish also held that 18 applies even nowadays.
So does the Mishno in Pirkei Ovos.
Yet when it comes to teaching Chumosh, Mishno & Talmud, many people are commencing at ages younger than delineated in this Mishno:- Hence why aren’t they doing likewise when it comes to Chuppo age mentioned in this very same Mishno?