I hate to break it to you all, but Myra might not even have been 13 yet when they married, according to this 1993 interview with Aspel:
"well she was 12 when i married her but she turned 13 about 3 days later"
It might be that he was confused about the dates, as according to Wikipedia their wedding was in December 1957, 5 months after her 13th birthday, but they married again in June 1958, about a month before her 14th birthday - after he'd finalized his divorce to Wife number 2, Jane Mitcham. It also says that Jerry was the cousin of Myra's dad, Jay, and had moved in with him and his family in 1956. Yuk.
I read somewhere else that she still believed in Santa Claus at the time.