Young Good Baseball Players

20-Year-Olds
Felix Hernandez is the only one in this age group, and he's taken his lumps to the tune of a 4.95 ERA. But Hernandez is 4-2 with a 3.70 ERA since June 1, and his 98/31 K/BB ratio suggests future growth.

21-Year-Olds
*Ryan Zimmerman, the Nationals' 3B, is batting .287/.478/.349 with 59 RBI. [Note: I added Zimmerman as an update - I unaccountably forgot him despite having added him to one of my rotisserie teams over the weekend]
*Flamethrower Jole Zumaya has a 2.08 ERA and 54 K in 43.1 IP and has been a key contributor to the Tigers' hot first half.
*Mariners SS Yuniesky Betancourt is playing everyday and batting .288.
*Matt Kemp is batting .281 and slugging .504 for the Dodgers.
*Melky Cabrera has a .358 OBP in 200 at bats for the Yankees.
*Others are still learning, like Matt Cain (80 K in 91.1 IP but a 5.12 ERA), or haven't had a complete shot yet, like Lastings Milledge, Fabio Castro, and Yusmeiro Petit.

22-Year-Olds
*Francisco Liriano is 10-1 with a 1.83 ERA and 102 K in 88.1 IP.
*Brian McCann is batting .343/.506/.406 and has all but established himself as the best catcher in the National League.
*Marlins starter Josh Johnson is just short of the innings for the NL ERA lead but would be out in front with a 2.21 mark and 74 K in 85.2 IP.
*Scott Kazmir is 10-6 with a 3.27 ERA and 125 K.
*Hanley Ramirez' batting average has dropped off to .271, but he's scored 69 runs and stolen 26 bases playing everyday as the Marlins' SS.
*Huston Street has 19 saves and a 37-8 K/BB ratio. Street's ERA is 1.74 since June 1.
*Jose Lopez is batting .280, slugging .454 and has 58 RBI as the Mariners' everyday 2B.
*Prince Fielder is slugging .479 and has 16 HR and 46 RBI.
*Jeff Francouer has come down from last year's rookie sensation, but is at least a reliable RBI man, with 17 HR and 63 RBI in the first half.
*Jeremy Hermida has been injured, but when healthy the Marlins' OF has posted a .378 OBP.
*The Marlins' Scott Olsen's 4.24 ERA is 20th in the NL.
*Jon Lester is 4-0 with a 3.06 ERA and 30 K in 32.1 IP in six starts with the Red Sox.
*Matt Capps has a 3.21 ERA and a 35-5 K/BB ratio in the Pirates' bullpen.
*Ambiorix Burgos has reclaimed the Royals' closer job and now has 14 saves and 43 K in 40.2 IP. With a 5.98 ERA and 8 blown saves it would be hard to call Burgos a success, but he shows promise.

Other 22-year-olds with more mixed or incomplete results so far: Cole Hamels, Nick Markakis, Dioner Navarro, Brandon McCarthy, Craig Hansen, Mike Pelfrey, Kyle Davies, James Loney, Howie Kendrick, Rene Rivera, Zack Greinke.

23-Year-Olds
*Joe Mauer is a leading candidate for the AL MVP, batting .378/.535/.446 with good defense behind the plate.
*David Wright, of course, is batting .316/.575/.386, has 74 RBI, and has been arguably the best player on the best team in the National League.
*Miguel Cabrera has been even better, at least with the bat: .334/.566/.432, with 25 doubles and 51 walks.
*Jose Reyes leads the majors in runs, steals and triples and the NL in hits.
*The AL leader in runs is Grady Sizemore, .291/.516/.363, with 46 extra base hits.
*At 10-4 with a 3.01 ERA, Justin Verlander has been a crucial contributor to the Tigers' improvement.
*So has Jeremy Bonderman, with a 3.46 ERA and 111 K and just 6 HR allowed.
*Rickie Weeks has scored 65 runs, stolen 17 bases and posted a .361 OBP (due largely to leading the majors in being hit by pitches) while playing second for the Brewers.
*Ervin Santana is 10-3 with a 3.96 ERA for the Angels.
*Jered Weaver is 6-0 in six starts, with a 1.12 ERA and a 36-7 K/BB ratio and just 23 hits allowed in 40.1 IP.
*Robinson Cano was batting .325 before he got hurt.
*Josh Barfield is batting .289 with 15 doubles and 12 steals as the Padres' everyday 2B.

Other less successful 23-year-olds: Zach Duke, JJ Hardy, Ronny Cedeno, Yadier Molina, Chris Resop, Ricky Nolasco, Anderson Hernandez, Casey Kotchman, Andrew Sisco, Jeff Mathis, Gavin Floyd.

24-Year-Olds
*Carl Crawford is batting .319/.521/.359 with 32 steals and 55 runs scored for Tampa.
*Francisco Rodriguez has 21 saves, a 2.89 ERA and a 47-10 K/BB ratio in 37.1 IP as the Angels' closer.
*Chris Ray has 22 saves and a 3.19 ERA as the O's closer.
*Mike Napoli is batting .286/.579/.412 in 140 at bats as the Angels' catcher.
*Ian Kinsler, when healthy, is batting .320/.553/.379 as the Rangers' SS.
*Rocco Baldelli, when healthy, is batting .315/.537/.373.
*Aaron Hill is batting .297 with a .344 OBP alternating between second and short for the Blue Jays.
*Wily Mo Pena, when healthy, has batted .321/.482/.370.
*Dontrelle Willis has a 3.94 ERA but should remain one of the NL's premier pitchers after winning 22 games in 2005.
*Zach Miner has added to the Tigers' wealth of young arms with a 6-1 record and 2.57 ERA in 7 starts.
*Chad Cordero has 13 saves and 43 K in 42 IP, coming off a tremendous season in 2005.
*Conor Jackson has a .370 OBP and 15 doubles as the D-Backs' 1B.
*Adrian Gonzalez is slugging .457 as the Padres' 1B.
*Manny Delcarmen has a 3.52 ERA and a 21-7 K/BB ratio and just 1 HR allowed in 23 IP for the Red Sox.

Other less successful 24-year-olds: the effective but injury-plagued Rich Harden, Jhonny Peralta (60 runs, but a comedown year with the bat), Willy Taveras, Oscar Villereal (8-1 but not that effective for the Braves), Ian Snell, Nate McLouth, Paul Maholm, Oliver Perez, Brian Anderson, Jesse Crain, Fernando Cabrera, Matt Murton, Kameron Loe, Brad Thompson, Brandon Watson, Corey Hart, Victor Diaz, Jerome Williams, Mark Teahen, Franquelis Osoria.