Source and citation: "Jerry Lee Lewis was an SOB Right to the End" by Bill Wyman (the author, not the musician).
So by you it's immoral but it's OK as long as you're famous enough. Cool.
As has been said, that kind of thing (marrying very young, and to cousins) was not unheard of at that time in that place in that culture - Jerry Lee himself first married at 16, which would be seen as underage in most places today. And the author of the piece casually mentions that Jerry Lee's sister first married at 12, then again at 15 ... no mention of clandestine schemes to accomplish this (though I'm guessing maybe Jerry Lee himself would have had to sneak a little because of the familial living situation). Then of course, there was Elvis and Priscilla ... . That Jerry Lee thought it would be ok to take his very young wife along on his tour of England shows how at odds his native culture and mindset was to that of most other places in the English speaking world.
I don't look favorably on it myself, of course, and I don't view it as a healthy thing for girls to get married at such a young age ... could be seen as a culturally sanctioned form of abuse - legal, but wrong. There's a lot of stuff that's wrong, that was once legal. And, technically, what Lewis did wasn't actually pedophilia, which would be sex with pre-adolescents. It might be termed hebephelia, which would apply with young adolescents. But those terms also imply "strong, persistent sexual interest" in such age groups, while Jerry Lee appears to have been an equal opportunity abuser
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