The very simple fact of the matter is that it IS legal in many, many place to have sex when you're 17, 16 or even 14. There are places in the USA where you can legally get married, with your parents' permission, when you're 14.

The very simple fact of the matter is that 18 has nothing to do with the actual legality issue in most parts of the world. Eighteen is a number plucked up by the United States Senate as being legal age to view sexually explicit material. It is NOT that age of consent in many states. Don't believe me? Go to Utah, Louisiana or Texas and ask a local judge what the state law is about age of consent. You certainly won't get 18 as an answer.

The funny thing to me is that, even though these people are old enough to consent to have sex, they're still not old enough to look at porn and explicit stories on the internet.

I have said it once and I'll say it again. America's outdated views of morality and purity of age in their effort to "protect the children" is archaic and should be changed. There isn't much difference between a 16 year old and an 18 year old, except what's written on a piece of paper somewhere. There's also not much difference between an 18 year old and a 21 year old, either, except for another excessively harsh and outdated law.