Satchel Paige, who made his debut for the Cleveland Indians in July 1948, two days after his 42nd birthday. He was also the oldest player ever, pitching his last game in 1965 at age 59, and allowing only one hit over three innings. [There's some dispute about his exact birthday - he may have been as much as six years older than the above figures!]

Of course, before he joined the majors, he was a star in the Negro Leagues. Since the end of the color bar, Diomedes Olivo began his Major League career on September 5, 1960 with the Pittsburgh Pirates, at age 41, while Joe Strong debuted for Florida in May 2000 at age 37. In comparison, Jim Morris [of 'The Rookie' fame] was a relative baby at only 35. :-)

Joe Strong = 史東