So much wrong in what you state the allthewhat
Firstly,
well, if 13-year olds want to have anal sex they should be given the instructions to do it safely" as a reasonable seeming solution.
then of course you're going to end up at "why shouldn't a 13-year old girl have anal sex?
^ doesn't relate in any way to what's in that article, have you read it? It doesn't mention the reality of anal, that it can cause serious harm, it's seriously biased and extremely dishonest.
I do believe that curious minds should find answers. The truth...not some dangerous porn that sounds like its been written by a child and purporting to be fucking cool , penned by some pornographer.
Yes, I do agree that there should be answers, which is why I've told teens the very dangerous risks of serious harms from anal, that the rectum is in no way designed to receive anything up it, only to expel waste and incompatible with hygiene and bodily safety. If you want to try it that you should be with someone you know very well and trust at least 100%, and even then it may hurt or cause bleeding.
Unsurprisingly, it didnt appeal! They were shocked and thought vagina and rectum had the same biology. 
How can any grow up not knowing that basic fact?
We seem to be floating along on myths and lies.
How very progressive.
I'm all for openess, access to facts, but that wasn't it. Miles from it.
Its heavily biaised and dangerous clap-trap for girls.
The fact it talks about girls, and guys. So girls, underage girls, yes, under age, not technically, actually underage and illegal, rape. Not even mentioned.
Not a whisper of safeguarding. All promoted,and normalised abuses.