In which legal jurisdiction and culture? Many or most website are have users from many locations.
Is the header a json encoded map from country code to age rating?
The US. If they want to serve users in other countries, or if certain states make their own rules, it's business as usual whether to serve different content there or serve a different header or take the legal risk.
The US. If they want to serve users in other countries, or if certain states make their own rules, it's business as usual whether to serve different content there or serve a different header or take the legal risk.