"Porn with actors who look younger then 18 is also forbidden (even when there is proof that they are 18+)."
It of course becomes difficult to apply a law such as this. For example, what looks young to one person, looks older to another --so in these kind of cases an offence might effectively be termed an 'affront to the public conscience'? But laws are often arbitrary and imperfect.
Another difficult law in the United Kingdom is that 'extreme pornography' is illegal. What is extreme is not clearly defined --it could mean very hard BDSM, or it could simply mean gagging. Or if the models become visibly and genuinely upset in video? I read of one arrest that was made in Northern Ireland (part of UK) on the basis of this law.
So what do we do? How do we best protect ourselves and maintain a safe environment? I would say we need to use a little common sense, and, as I said before, to set limits in one's own mind, to be aware of the issues and the complexities, the laws of one's own country and, of course, international law.