[Answer] After Queen Elizabeth II, who is next in line for the British throne?

Step 1 : Introduction to the question "After Queen Elizabeth II, who is next in line for the British throne?"

...Prince Charles, the oldest son of Queen Elizabeth II and Prince Philip, is the heir apparent to the British throne. His mother became queen when he was only three after the death of his grandfather King George VI in 1952. As Elizabeth's oldest child, Charles became the heir apparent to the British throne and received the title of Duke of Cornwall. Charles was also destined to become Great Britain's oldest heir apparent, with his mother remaining queen for more than six and a half decades. His younger siblings are Princess Anne, Prince Andrew and Prince Edward. He is the father of Princes William and Harry.

[Answer] How old was Mary Stuart when she ascended to the throne of Scotland?

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