William Pitt, the Younger, became Britain's prime minister in 1783 at the age of:
18
24
35
67
77
24. William Pitt, the Younger, became Britain's prime minister in 1783 at the age of 24. He was one of Great Britain's greatest peacetime leaders and served a prime minister from 1783-1801 and from 1804 until his death in 1806. Pitt was the son of William Pitt the Elder, who served as prime minister from 1766 to 1768.