Not all pro porn requires age checks. That made in the US certainly does, but the requirement isnt universal. Nor is the definition of porn. Many european "art" websites (nudes, generally no sex acts) are not pornographic and feel no need to maintain such records. Playboy would probably not be considered "porn" in many jurisdictions, at least in terms of production. What it is when found on your hard drive while sitting in the US is another matter.