See the visit of Jerry Lee Lewis with his wife who was not only underage (here) but also. if I remember rightly, his blood cousin.
I saw a biopic of Jerry Lee Lewis on BBC4 a while ago. Yes he did marry a thirteen year old cousin - not a first cousin. It wasn't unusual in the region where he lived. They did eventually divorce but she always spoke well of him, wild man that he was. When he came here he brought her with him, the press found out her age & he was no longer welcome.
The country star, Loretta Lynn (Coal Miner's daughter), married at 14, had three kids by 18, and I think she remained married to the same man for life.
Floo probably doesn't watch BBC4 but as well as great music, it's quite an education!