Winston Churchill was 65 when he became prime minister of Great Britain in 1940. He became prime minister again in 1951 at the age of 76; when he left office in 1955 he was 80.
Konrad Adenauer became the first chancellor of the Federal Republic of Germany in 1949 at the age of 73. He remained chancellor until his retirement in 1963 at the age of 87.
In 1958, at 68, Charles de Gaulle was elected the first president of the Fifth Republic of France. He held this office until retiring in 1969 at the age of 78.
In 1994, Nelson Mandela -- after 27 years in prison -- became the first democratically elected president of South Africa. He was 75 at the time.
And of course, Ronald Reagan, now commonly ranked among the greatest American presidents, was 69 when he became president of the United States in 1981 and 77 when he left office in 1989.