How MLS's first true star to penetrate pop culture came in a 14 year old, Freddy Adu in 2004.
Sources:
A 12-YEAR OLD’s AMAZING FEAT by Jason La Canfora for Washington Post. https://www.washingtonpost.com/archive/politics/2001/08/25/a-12-year-olds-amazing-feat/9923da6b-4f3d-4f9a-bd31-bb67449c437f/
READY FOR FREDDY? AT 14, FREDDY ADU IS ALREADY THE HIGHEST PAID AND MOST CELEBRATED PLAYER IN MLS by Grant Wahl for Sports Illustrated: https://www.si.com/vault/2004/03/29/366282/ready-for-freddy-at-14-freddy-adu-is-already-the-highest-paid-and-most-celebrated-player-in-mls-now-its-time-for-him-to-play-his-first-game
Freddy Adu assist against Argentina in 2003 u20 World Cup: https://www.youtube.com/watch?v=sMk33g4PthI
Seriously, What Happened To Freddy Adu by Noah Davis for Grantland: https://grantland.com/the-triangle/freddy-adu-us-national-team-mls-2015/
Much Adieu About Freddy by Timothy DeSchriver: https://www.researchgate.net/publication/289978174_Much_Adieu_about_Freddy_Freddy_Adu_and_Attendance_in_Major_League_Soccer