Mike Trout
On April 17, 2015, Trout became the youngest player in MLB history to reach 100 home runs and 100 stolen bases. He was 23 years and 253 days old when he reached the milestone, passing the previous record-holder, Alex Rodriguez, who had achieved it at the age of 23 years and 309 days in 1999. Trout led off the 2015 MLB All-Star Game with a home run, becoming the fourth player in All-Star Game history to do so. For the second year in a row, Trout won the All-Star Game MVP Award, becoming the first player ever to win it in consecutive years. On September 22, Trout hit his 40th home run, becoming only the second Angels player to hit 40 home runs in a season. Trout led the AL in WAR for the fourth straight year.
Julio Urías
Urías pitched two innings of relief in game five of the 2016 National League Division Series, picking up the win. At 20 years, 62 days old he became the youngest Dodgers pitcher to ever pitch in the post-season. He was two weeks younger than Don Drysdale was in game four of the 1956 World Series. He was also the fourth youngest pitcher in MLB post-season history, behind Ken Brett (1967 World Series), Bert Blyleven (1970 ALCS), and Don Gullett (1970 NLCS and 1970 World Series). He became the youngest pitcher ever to start a post-season game when he started game four of the 2016 National League Championship Series. He allowed four runs in only 3 innings in the game.