Except you're the one missing the context. What they're trying to do with that provision is force everybody to check if someone is designated as a minor so they can't claim that they didn't know. If they let you choose whether to check then you choosing not to check could make it harder to punish you when there is a dispute about whether something should have been shown to a minor, so they wrote it in a way that lets them punish you more easily if you check and also punish you more easily (for not checking) if you don't.

The problem then follows that everyone is stupidly required to check even when it's totally unambiguous there is nothing to be done with the information, because of the risk of someone trying to punish anyone who doesn't check in order to prevent the precedent that some people aren't required to and correspondingly can't be assumed to have knowledge of someone's age.