The youngest MLB player ever was Joe Nuxhall, who was 15 years and 316 days old when he debuted for the Cincinnati Reds on June 10, 1944, at Crosley Field.
At the time, Nuxhall had just finished his freshman year of high school as a big but wild left-handed pitcher.
Despite his young age and raw talent set, though, the Reds had signed Nuxhall to a major league contract that January as a way to fill out a roster depleted by World War II, with many active MLBers having enlisted or been drafted into to the armed forces.
With the Reds trailing 13-0 in the ninth inning at home against the St. Louis Cardinals on that fateful June day, Reds manager Bill McKechnie brought in Nuxhall to finish up.
But the teen pitched true to form, giving up five runs on two hits, five walks, and a wild pitch.
That was it for Nuxhall in the majors until 1952, when he was still just 23 years old. He would go on to pitch 16 years in the majors, almost all with the Reds, punctuated by brief stops with the Kansas City Athletics (1961) and Los Angeles Angels (1962).
Nuxhall stepped right into the Reds broadcasting booth in 1967 after he retired, and he stayed there through 2007, teaming with Marty Brenneman for much of that time.
Ironically, the youngest MLB player the game has ever seen eventually became known as “the old lefthander” during his career in the booth.
Nuxhall died in November of 2007 after a battle with cancer.