The United Kingdom has long been trying to introduce age verification laws for pornography sites. A system using passports, credit cards, and other means was supposed to...
Not to mention it is all based on the questionable assumption that porn is somehow harmful for teens to watch but the exact same porn is not harmful for adults.
Neither is a teen freely sending a nude selfie of themselves to their teen SO.
Many family photo albums feature naked kids in various stupid situations that were just thought to be cute and funny at the time, which would nowadays melt peoples brains if they'd hear about it, and certainly would fall under the same laws that would punish the teen in the other example.