Japanese manga magazines usually have distinct demographic targets narrowed by age and sex. This is usually evident within the title, like Shōnen Magazine, Shōnen Jump, Shōnen Gangan, Shōnen Champion, Shōnen Sirius, and the list goes on. That said, many readers will walk across the aisle and read manga even if it isn't "for" them. There are plenty of men reading shōjo and women reading shōnen manga.