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.
Joe Nuxhall
Nuxhall remains the youngest person to play in a major league game in history. During his lifetime, it was believed that a 14-year-old named Fred Chapman pitched five innings in one 1887 game. However, in 2009, the Society for American Baseball Research discovered that this player's name and age were both incorrect. The 1887 player was actually named Frank Chapman, and he was 25 years old at the time of his only major league appearance. There have also been sources listing Billy Geer, who played for the 1874 New York Mutuals of the National Association, as having a birth date in 1859, but this is questionable as well, as is whether the National Association was a major league.