Walter Johnson
Bob Feller
Hal Newhouser
Early Wynn
Jim Palmer

I wonder how many Hall of Fame hitters debuted in the big leagues as teenagers. The only one that jumps to mind is Robin Yount. It would be interesting to find out if teenage hitters have better careers than teenage pitchers (the assumption there being that teenage pitchers get overworked and burn out early).

Also, one assumes that players hit the majors as teenagers because great things are expected of them. It would be interesting to see how often those great things actually happen, or if it can be said that these players are being rushed. I know that it's generally true that truly great players hit the majors in their very early 20s (Edgar Martinez being perhaps the only exception), and that the likelihood of a player developing into a Hall of Famer is greater the sooner they hit the bigs (I may be distorting that truism somewhat). But I wonder if that's a trend that reverses itself on the other side of 20.

48 future HoFers played as teenagers, three of whom went into the Hall as managers:

Name category MinOfAge
Al Lopez Manager 19
John McGraw Manager 18
Leo Durocher Manager 19
Christy Mathewson Player 19
Harry Heilmann Player 19
Harmon Killebrew Player 18
Hank Greenberg Player 19
Hal Newhouser Player 18
George Kelly Player 19
George Davis Player 19
Freddie Lindstrom Player 18
Eddie Collins Player 19
Al Kaline Player 18
Don Drysdale Player 19
Jimmie Foxx Player 17
Chief Bender Player 19
Catfish Hunter Player 19
Cap Anson Player 19
Brooks Robinson Player 18
Bobby Doerr Player 19
Bob Feller Player 17
Bill Mazeroski Player 19
Babe Ruth Player 19
Amos Rusie Player 18
Early Wynn Player 19
Nolan Ryan Player 19
Waite Hoyt Player 18
Ty Cobb Player 18
Tris Speaker Player 19
Travis Jackson Player 18
Sandy Koufax Player 19
Sam Crawford Player 19
Rogers Hornsby Player 19
Roger Bresnahan Player 18
Robin Yount Player 18
Herb Pennock Player 18
Pud Galvin Player 18
Jim Palmer Player 19
Nellie Fox Player 19
Mickey Mantle Player 19
Mel Ott Player 17
Johnny Bench Player 19
John Ward Player 18
Joe Morgan Player 19
Joe Kelley Player 19
Joe Cronin Player 19
Walter Johnson Player 19
Ray Schalk Player 19

http://retrosheet.org/boxesetc/B09090ARI2003.htm

Jackson was born in Germany - but unfortunately, the time zone thing works to his disadvantage.

As far as your chart above goes, Jackson was never 19 years old in the majors. His first game was this.

I saw that one but Johnson came out as 39 in my analysis. Jackson registers at 19 because I use 7/1 as the cutoff date (same method as Baseball-Reference, I believe).