Age of consent in the United States is set by each individual state. The range of age of consent for all the states is between 16 and 18, with most states at 16. Here is the guide if you want to see what it is in your state. http://www.ageofconsent.us/
it varies from state to state, but for the majority it's eighteen. Some it's seventeen, some it's sixteen. If you're asking this because you're planning to get intimate with someone who is under eighteen in america, check what the age of consent is for the state you'll be in.
The youngest age in the USA is 14 in South Carolina (16 if the partner is over 18). Most states, it's 18 but most also have "Romeo and Juliet" laws that reduce the age for a partner that less than two years older. As an attorney, I believe the age of consent should be no older than 14. Every case that I've ever seen pursuing statutory rape is the woman's father trying to bully her by attacking her boyfriend. Other than actual children or the mentally infirm, statutory rape is archaic holdover from when unmarried women were property of their fathers and brothers.