What makes you think the age of consent is gonna remain 18? They are already pushing for 12.
Age of consent for sex is not the same as the age that someone can star in porn.
Interesting fact: 18 is the age of consent for porn not because that is the age of consent for sex (most states have lower ages of consent) but because it's an age that works better in terms of prosecutions. It's a lot easier to tell the difference between an 18 year old and a 15 year old than it is to tell the difference between a 16 year old and a 14 year old.
So, though it might be legal in a lot of places to have sex with a 16 year-old, it would be illegal to film the sex.
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.