An interesting story was told me by a couple who, at age 50, had been married 35 years. Seems they had been boy/girlfriend since elementary school and always said they would be married one day. In the course of time, the girl's mother died, leaving her father to raise the child. Then when she had just turned 15, he was diagnosed with inoperable cancer.
The children's parents got together and told them that if they really wanted to get married, the parents would help. They did, and so they did. They had their first child before their 16th birthdays, and when I knew them they seemed to be a very tight couple. Their first-born son seemed to be the same age as they.

(You led the way, Steve S!)