Its already illegal to show adult material to minors. If they were about enforcing laws properly they'd just do that. For instance a court ruling that adult material isnt allowed on the internet, since you can't effectively ID visitors.
Anyone could just make a fake ID though, so what did they do? Make creating fake IDs a crime. If we can lie about our age to the OS, they'll make it illegal to do that as well.
This is an obvious move to reduce computing freedom.