The past two years have seen a wave of young position players come to the majors and contribute immediately, often becoming massive stars in their first or second seasons. The top two candidates for the National League MVP Award this year are a sophomore, Kris Bryant, and a rookie, Corey Seager, both of them well-rounded offensive players who add value on defense as well. Francisco Lindor and Carlos Correa are two of the 10 best players in the American League, and they're just 22 and 21, respectively. Four of the top five players in the AL by Wins Above Replacement (WAR) are age 26 and under, led by 24-year-old Mike Trout -- now the 12th player in MLB history to post two 10-WAR seasons. (All data in this article is courtesy of Baseball-Reference and its invaluable Play Index search tool.)
This is all part of an ongoing trend toward younger position players producing more -- taking away some of the older players' share of overall production in the process.
The average age of players reaching 5-plus WAR has dropped by about 18 months from the 1997-2006 period to the 2007-2016 period; it peaked at 29.4 years in 1999, and in 2016, it has returned to its low for the time period of 27.4 years.