Step 1 : Introduction to the question "How old was Mary Stuart when she ascended to the throne of Scotland?"
...Mary Stuart was all of 6 days old in 1542 when she ascended to the throne of Scotland at the death of her father. She traveled to France for her childhood and education while agents ruled in her stead. When she was old enough, she became queen consort for a short time in France before she returned to take her throne in Scotland. At one point, she successfully claimed the English crown. Scottish nobles forced her abdication in 1567 and she sought protection from her cousin, England's Queen Elizabeth I. Instead, Elizabeth had her arrested and imprisoned until her execution in 1587. Source: Biography.com