Many states have legal ages of consent for sex below 18. There is a difference between legal sex between boyfriend and girlfriend because of age and producing, starring in, and purchasing porn. Those doing that are engaging in legal, contractual obligations. Jim and Joan down the street banging in the back of a car are doing no such thing.
I understand that the age for starring in porn is 18. My question still stands....what makes you think this is not going to change. Many of the restrictions have been liberalized and continue to be. Give 'em an inch and they take a yard. What was "X" rated when I was a teenager is now R rated. That will soon be PG13. lol...actually a sad state of affairs.