@izzythepush,
The first "x-film" I saw, was "The Silent". It was rated for 18 and above, had even policemen controlling the age in my native town (since I was only 14 or 15 at that time, I just went in when they weren't there).
Later, this film was rated for 16 years olds ...
I think, the age limit of 18 is just for porn now.
The most X-rated films I've seen when I've been in England during holidays, there were no age controls in the cinema I went to in those days ...