It's illegal if an 18 year old had love with an 11 year old.
A 13 year old having love with an 11 year old is legal.
Then again, I think it's legal for a 16 year old to have love with an 11 year old.
love with an underage person is illegal if you're 16 or older. It is also illegal for two underage persons to have love with each other. However, they won't be persecuted as long as the love is wanted and between two persons at the same maturity level.
At least that's how it is where I live. Don't know about the US though...
EDIT: LOL! In Mexico, the age of consent is 12 or 13, depending on which state. In Angola, the limit is 9 (!!!). In the Antarctic, there is no age limit :D