Notes from the Past: Marriages

Lady Georgiana Cavendish
and Elizabeth Foster Cavendish
(below) both married at 17.

Western history is often portrayed in romances as a place where youngsters are married off to elderly personages, innocent teen girls to grumpy men; youthful teen boys to robbing-the-cradle ladies. 

It is true that 12 was the legal age for marriage in the 18th century.

However, as stated by G.J. Meyer, during hard agricultural times in the 1500s, merchants and farmers actually married "in their mid-twenties or later." Even amongst the nobility, later marriages were not uncommon. Although Henry VII's mother was married at age 12 and bore Henry VII at age 13, she didn't bear any more children, likely due to complications with Henry VII's birth.

Medievals may have been callous (debatable), but they weren't stupid. If you wanted kids, you waited for maturity to hit. During the divorce between Henry VIII and his first wife, Catherine, those against the divorce argued that Catherine's prior marriage to Arthur, Henry VIII's brother, was never consummated--therefore, the marriage never existed--therefore, Henry VIII had no reason to whine about the unlawfulness of marrying his brother's wife. The argument for non-consummation has merit: Arthur was sickly and may not yet have undergone puberty despite Catherine and Arthur both being approximately 15 when they married.

Elizabeth--or Bess--then moved in with
Georgiana and her husband whom Bess married
after Lady Georgiana's death.

However, while not condoning marriages to early adolescents (and not all parents of the past did), the denouncement of the act as perverse would have confused anybody up until the 20th century. When middle-age is 35, old-age is 50, and princes are leading armies at 18, getting married at, say, 13 wouldn't seem quite so strange and icky as it does now.

It still wasn't the norm, however useful the trope is in fiction.