My great grandfather married my great grandmother (his first cousin) when he was 24 in the Army and she was 13. Apparently, in my family tree, anything goes.
h34r:
They stayed married for 80 years btw until he died at age 104. Never had a goofy looking kid or anything even though they were first cousins. I guess love breaks down all barriers.
For me personally, anything under 18 would bother me, legal or not.