youngest prime minister to leave office was the Duke of Grafton, who retired in 1770, aged 34. The oldest was Gladstone, who was 84 years at the time of his final retirement in 1894. Age differences of outgoing and incoming PMs Greatest age difference — Lord Rosebery (born 7 May 1847) was 37 years 129 days younger than William Ewart Gladstone (born 29 December 1809) whom he succeeded after the final retirement of the latter in 1894. Smallest age difference — George Canning (born 11 April 1770) was 57 days senior to Lord Liverpool (born 7 June 1770), whom he succeeded after Liverpool retired in 1827. Canning and Liverpool were one of four pairs of immediately consecutive prime ministers who shared a same birth year, the others being: William Pitt the Younger (served 1783–1801 and 1804–1806) and Lord Grenville (served 1806–1807), both born in 1759 Lord Aberdeen (served 1852–1855) and Lord Palmerston (served 1855–1858 and 1859–1865), both born in 1784 Harold Wilson (served 1964–1970 and 1974–1976) and Edward Heath (served 1970–1974), both born in 1916 The decade of the 1730s was the most productive for births of five future prime ministers: Lord Rockingham (born 1730, served 1765–1766 and 1782), Lord North (born 1732, served 1770–1782), the Duke of Grafton (born 1735, served 1768–1770), Lord Shelburne (born 1737, served 1782–1783), and the Duke of Portland (born 1738, served 1783 and 1807–1809). Longest-lived The longest-lived prime minister was James Callaghan, Baron Callaghan of Cardiff, who was born on 27 March 1912 and died on 26 March 2005 at the age of 92 years 364 days, which was the day before his 93rd birthday. Prior to this the longest-living prime minister was Harold Macmillan, 1st Earl of Stockton, who was born on 10 February 1894 and died on 29 December 1986 (aged 92 years, 322 days). Of the seven former prime ministers currently alive, the oldest is John Major (born 29 March 1943), who is years old. If he reaches his 93rd birthday on , he will surpass Callaghan's record and he will become the longest-lived prime minister. Shortest-lived The shortest-lived prime minister was the Duke of Devonshire, who was born on 8 May 1720 and died on 2 October 1764 at the age of 44 years and 147 days. Longest-lived after office The prime minister who lived the longest after leaving office for the final time was the Duke of Grafton, who