Spinster at 15...

Apparently, it was normal to get married by 12 or 13 during the 18th century... however, Marie Antoinette of Austria, who married Louis the XVI of France, was 15 and he was 16. It was an arranged marriage and they didn't have their first child until 7 years after they were married when she was 22. Supposedly, Louis the XVI was faithful to her, even though it was de rigueur for the kings to be unfaithful to their queens.