On September 25, 1965, 59 year old Satchel Paige of the Kansas City A's pitched 3 scoreless innings. From the article:
"Satchel Paige never worried much about Father Time.
“Age is a question of mind over matter,” begins the apocryphal quote attributed to Paige. “If you don’t mind, it don’t matter.”
Paige, as he usually did, proved his words true. On Sept. 25, 1965, Paige became the oldest player to appear in a big league game when he started on the mound for the Kansas City Athletics.
Paige, born (according to most sources) July 7, 1906 in Mobile, Ala., dominated Negro Leagues baseball in the 1920s and 1930s when the color barrier prevented African Americans from playing in the big leagues. By the time Jackie Robinson broke the barrier in 1947, Paige was 40 years old – yet still an effective pitcher.
Cleveland Indians owner Bill Veeck signed Paige midway through the 1948 season, making him the first African-American pitcher in the American League. Paige went 6-1 with a 2.48 earned-run average down the stretch, helping Cleveland win the American League pennant and eventually the World Series."