Private companies now can link all your online activities to you. Not an advertisement ID, but directly to you and your loans and your health data and whatever they're selling in the black market. Every data breach is a 100 times. It was already almost possible to directly know about you by buying data, now it's easier.

The point of this is not to verify age really. It is to verify identity. There's no way to prove someone is some age without presenting a legal ID.

Also, it's not just porn, facebook, online gambling etc. It is the OS based on some bills. So ALL your activities.