Another interesting Ask BA at Baseball America. This week Jim Callis talks about players that made their major league debut at seasonal age 20 (as of June 30) since 1990. He mentions five players that he thinks could be regulars by the end of the season; Royals righty Zack Greinke (20), Devil Rays shortstop B.J. Upton (19), Braves third baseman Andy Marte (20) and Dodgers lefty Greg Miller (19) and amazingly Devil Rays outfielder Delmon Young (18) who was just drafted last year.