What are you talking about, this is not what it says.
It says that countries should apply their age of consent laws fairly regardless of the gender of the people involved or whether they are married. This is because in some countries it's a higher age of consent to have gay sex than it is to have straight sex. In other countries some people can circumvent age of consent by marrying their victim. Even in some parts of America that's true. This point actually protects kids because it's against child marriage.
When it says "sexual conduct involving person below the domestically prescribed minimum age of consent to sex may be consensual in fact if not in law" it's talking about how in some countries (like Australia) the age of consent is 16, while in different parts of the US for example, it's 18/17 depending on where you are and how old the other person is. So the idea that the age of consent is a hard and fast "line" that everyone agrees on is not true, and different people may be able to meaningfully consent at 16, while others may not at 18+. And so when judging statutory rape cases it's important to listen to the "victim" and base your judgement off the harm caused to them. In some cases (let's say a 16.5 year old and a 17 year old) there may not be any real harm.
Teenagers often have sex with each other. So two minors having sex. I had friends who had sex with people their own age around 15. This is not pedophilia. So the point about "the enforcement of criminal law should reflect the capacity of persons under 18 to make decisions about engaging in consensual sexual conduct" is because you don't want a 15 year old kid to have to register as a sex offender because they had sex with another kid the same age, or took nudes of themselves.
Some common sense here PLEASE. It's about protecting youths from overzealous morality police. There are literally teens today who have been prosecuted for "child porn" because they had photos on their phone OF THEMSELVES nude.
We want to protect youths against predatory adults. Not to punish them for being horny teens. And I think the idea that "any sex under 18 is instantly pedophilia" is short sighted given that many countries the age of consent is not 18. In Australia, where I come from, it's 16 and that's normal. I still think it's creepy for an adult to hit on a 16 year old. But the fact it's legal here and pedophilia is NOT normalised here, indicates the somewhat (necessary but) arbitrary nature of the age of consent. Everyone matures differently so assuming everyone is automatically ready for sex at a particular age (and is definitely not at the same age) is unrealistic. THIS DOES NOT MEAN HAVING SEX WITH KIDS IS OK. But different people at stages of young adulthood (between 16-19) become ready for sex at different times. And the law needs to set a point for the age of consent, I understand. It's necessary for the purpose of law to try and make it unambiguous. At the same time we don't want to punish teenagers for experimenting sexually with each other.
