In Italy the age of consent is 14, it can go down to 13 if the partner is at max 15 years old, but it raises to 16 if the partner is a temporary or permanent authoritative figure, like a coach or a teacher.
18 is the limit at which it is allowed to publicly show or sell pictures/movies about that person naked or performing sexual acts.
I frankly feel that this is one of the very few cases where Italian laws get the facts right: thirteens would still (try to) have sex wether or not it was allowed.
I remember that I believed too that the age of consent was 18, and felt fine with it, so it was a little shock to discover that the limit was much lower. I later however got various data about how sexual expression/desire/maturity starts around that age (mine too, FWIW), so I reconsidered that this was indeed a case of a law just making common sense: you don't throw in jail a teenager just because of his/her natural impulses.
you don't throw in jail a teenager just because of his/her natural impulses
Well, in the general case, of course you do... at least, if you throw them in jail at all. Adults, too. Most crimes are natural impulses, at least for people raised in a given culture; acts that we are neither naturally inclined to do nor explicitly taught to do tend not to be common enough to be worth the effort to pass laws against.
With respect to age of consent laws in particular, I would say there's more than one relevant age threshold if we're going to bother regulating this...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.