I can completely understand why KB would ban under 18 anything. Unless you have a server in a country where the long arm of the US can't get to AND you have a staff committed to under 18 material, it is dangerous to post any underage sympathies and material.
When I was 14 I met a girl my age that I took an immediate liking to and when I asked her out, not only did it turn out that she was married, a lot of girls in the area her age were also committed or married. Suddenly, a light bulb went on in my head about a great many things. That was the way it was in the mid 1970's. The US federal government finally got around to banning under 18 film and pictures in 1978 and this only happened because Brooke Shields played a 12 year old prostitute in a movie and there were plenty of scenes where she didn't wear clothing. Then there was the Tracy Lords situation.
Tracy posed nude for Penthouse magazine a month before her 16th birthday and a year later she was the biggest porn star on the planet. The entire Tracy affair came to light because Tracy got a passport (to make a porn movie in Japan) using forged documents. Federal authorities were waiting for her when she got back and Tracy named names. It turned out that Tracy wasn't the only under 18 in porn, but she was the best known. The porn industry quickly tightened up their rules and cleaned house.
The "Me Too" movement, in 2017 claimed a victim of the earlier mentioned era. David Hamilton took artistic nude pictures of girls under 18 (published a number of books with the pictures) and he produced five films with this kind of theme. This happened from the mid 1970's to mid 1980's. When the whole Me Too thing went down, one of David's former models said that David did more than take pictures. David ended himself before a full investigation could ramp up.
In 1995, a major scandal happened in Belgium as it turned out that a number of government officials were trafficking and using girls. There is a great movie (The Memory of a Killer) about the scandal. As the trials happened, European countries began tightening their rules about age of consent as well as literature.
Finally, a Belgium like scandal is about to explode in England. It has been said that gangs of Arab men have been abducting and raping girls, and that's not the horrible part. English police have either been arresting and jailing people that spoke up about it or have warned people to keep their mouths shut about it, or else. Being that Prince Andrew has already been embroiled in one sex scandal, it is rumored in England that one or more royals are somehow connected to this whole thing.