Answered April 22nd, 2019

Madison Bumgarner becomes the second-youngest pitcher (behind Jim Palmer) to throw at least 8 scoreless innings in a World Series game.

Who was the last 21-year-old player with 8 IP and 0 ER in a World Series game?
Interpreted as:
Who was the last 21-year-old player with 8 or more IP and 0 ER in a World Series game?