Traditionally the age of consent in the US was 10. Now federal law says it is 16 for US citizens, regardless of where they are, meaning even if a US citizen is in a country with an age of consent of 15 they cannot legally have sex with someone under 16. Individual states can set the age of consent over 16, but they cannot over ride federal law, setting it lower would only be ceremonial. States have ages of consent set at 16, 17 and 18. Most of the world has age of consent set below 18, Canada in 2000 had the age of consent set at 14. I think 14 is a good number, it protects young children but doesn't needlessly demonize people for screwing fully self aware teenagers.