It is my understanding that the phrase “sweet sixteen and never been kissed” is an extension of the phrase “sweet sixteen.” Both are unattributed clichés from the early 20th century in the United States used to express a romanticised view of sixteen year old girls and often meaning very innocent and/or naive about sex. Since the early decades of the 20th century in the United States and the UK, the phrase has been used often in songs (e.g., “When You Were Sweet Sixteen,” Al Jolson; “Lady Killer,” lyrics by John Entwistle) and prose (e.g., Mary-Kate and Ashley, “Sweet 16 Never Been Kissed,” Harper Collins: Australia 2003; Ioda Munn, “Sweet Sixteen and Never Been Kissed”).