Well, the 'punishment' is not letting him use the service, which he wasn't supposed to be able to do anyway as a minor. It isn't like he is going to jail or being forced to pay a fine.
You seem to be arguing that you can't ever prevent minors from using your service, since you can only exclude them via your TOS and you can't enforce a TOS against minors.
This seems very similar to the arguments that "freeman of the land" use to argue that they can do whatever they want since they don't agree to be bound by laws.
