You are giving authoritarians benefit of a doubt for no good reason. Vagueness in such laws is usually to allow selective enforcement by the people in power and not for you (a regular user) to have an "escape hatch" from negative consequences of the law. The reality of the situation is that there are currently no other ways to enforce age checks besides asking for an id and any kind of theoretical parental-controls-configured browser headers are years away from deployment, best case.