There is reading material with nudity and sex for sale in Japan that you don't have to be an adult to buy.
You know them as those annoyingly lightsabre-censored manga, where the genitals seem to emit detail-obscuring light. It's obvious her vagina is being penetrated by a penis or the like, but the delineation is blotted out.
You don't have to be an adult to purchase those. But the ones shown in the image you replied to-- those are for adults only.