This article provides a detailed history of film classification, or age ratings, in Japan. It describes historical precedents for Eirin, the agency responsible for film classification in Japan, and key moments in Eirin’s organisational formation and reform. Drawing on multi-sited archival research and interviews with Eirin staff, the article recognises the importance of the US Production Code Authority as a model for Eirin’s formation during the United States’ occupation of Japan, but also argues against understanding age ratings in Japan as just another American import. By tracing earlier domestic precedents and by highlighting similar controversies overseas, the article considers the crucial role of both state and non-state actors, as well as international models and markets, in reforming film governance for youth spectators in Japan. Two exemplary scandals involving the Zigomar films in the early 1910s and the taiyōzoku (sun tribe) films in the mid-1950s demonstrate lasting concerns over youth that Eirin seeks to address. The article describes the redevelopment of the classification system in the late 1950s that underpinned an enduring form of now internationally-recognised regulation.