"I will never believe it.
"
OK, but your not believing it does not mean it did not happen. It was quite common, and didn't end until sometime in the 70s.
Also I disagree that sexual intercousre was as common then or as is it alledged to be today amounst teenagers. Girls that did were tagged easy, it was a dsgrace and the girls did not want that tag. Lot of petting, very little intercourse.