IDs and age are already checked if the internet access is bought (DSL, cable, whatever). Even if you buy a mobile phone SIM and contract, ID is checked.
In most routers there is a check box regarding letting no adult classified media through, which should filter the most famous sites. (a click).
Parents are responsible for their offspring and minors in reach. If they neglect their responsibility they can be charged. If they handle them a bottle of booze or the keys to their car that is on their responsibility.
WLANs have keys. Phones have Pins.
Compare the age verification app to the introduction of electronic medical record (ePA in Germany). The significant security features and fine granular controls that were used to advertise its introduction, were removed for simplicity when released.
And since most adult sites have user forum or comment function there very soon will be the call for identification ability.
This initiative (like a lot of others of the EU) opens just a lot of new problems (new threats, attack vectors, gives incentive for identity theft, makes services more fragile, introduces new parties and middlemen).
It won't solve the problem, that certain percentage of people have forked, that better did'nt.