Stephen and I discussed this in RinkChat last night. I am positive I'm not hallucinating, but the last time I remember seeing the 'R' rating's cut off age 18 was when I was living in Germany; we saw movies on an American military base. The ratings were the same there as here (not to be confused with Germany's own rating system, which didn't apply to the movies we got on our own base), but maybe some kind of law or policy required their interpretation to be different. *shrug*