I think I should point out that in the US there are 2 different ages of consent and both laws are still in the books in many states.
1- the one we all think of the age a person can say I want to have sex with you
2- the forgotten one a parent can be asked for permission to have sex with their child - this one was used more about giving permission to marry (sex imply d) and really how many time do you think someone asked daddy "hey can I have sex with you little girl?"
But as to the question 16 is the lowest I would go and even wonder about that.
Also a with-in 6 months grace rule for and partner over 18.
Also a rule stating that teachers and other authority figures can not have sex with anyone they hold a position over.