Who is the youngest player in MLB?
Joe Nuxhall
In addition to his 40 years of broadcasting Reds games, Nuxhall is most remembered for having been the youngest player ever to appear in a major league game, pitching ​2⁄3 of an inning for the Reds on June 10, 1944 at the age of 15years, 316days. Called upon for that one game due to player shortages during World War II, Nuxhall eventually found his way back to the Reds in 1952, and the National League All-Star team in 1955 and 1956. Long known as "The Ol' Left-hander", he compiled a career earned run average of 3.90 and a record of 135–117 during his 16-season career, with all but five of his victories being earned with the Reds. Nuxhall died in 2007 after a long battle with cancer.
Jason Marquis
As a 12-year-old, Marquis pitched his team to third place in the Little League World Series with a no-hitter. He is one of only a few ballplayers to have played in both a Little League World Series and a Major League World Series. He also pitched his high school team to consecutive New York City baseball championships. Marquis was drafted in the first round out of high school by the world champion Atlanta Braves, and reached the majors as a 21-year-old in 2000.