Who is the youngest prime minister?

The youngest British prime minister at the time of his appointment was William Pitt the Younger, who was appointed to the office at the age of 24. He became prime minister in 1783 and remained in office until 1801. He was reappointed to serve from 1804 to 1806.

Pitt was followed by Robert Banks Jenkinson, Earl of Liverpool, who became prime minister at the age of 42 and served from 1812 until 1827, when a stroke forced him to resign. The youngest prime minister since Lord Liverpool is David Cameron, who became prime minister in May 2010 at the age of 43.