Are you guys really worried about an 18 year old struggling in A-ball? Go back to 2000 and count up all the guys who are even talented enough to have played in A-ball as 18 year olds. We're talking like 10 guys a year. Guys who do well are guys like Fernando Martinez, Justin Upton, Jose Tabata, et al.
I'd be kind of happy that all of his hits are doubles. 18 years old! He should be in high school right now!
Let's play a game. I'm going to name all the 18 year olds who have put up a .700 OPS in A-ball since 2000. Minimum 200 AB.
2000: Chris Snelling, Carl Crawford
2001: Grady Sizemore, Edwin Encarnacion, Jose Reyes, Miguel Cabrera
2002: Gregor Blanco, Andy Marte
2003: Felix Pie, B.J. Upton
2004: Adam Jones, Delmon Young, Daric Barton
2005: No one.
2006: Jose Tabata, Fernando Martinez (192 AB), Justin Upton
2007: Carlos Triunfel (17 years old--152 AB), Chris Marrero, Bill Rowell
That's quite a list. Only flops are Marte and Blanco and Snelling. And Snelling only because of injuries. And Blanco is still only 24 and fast as hell so he's not done yet. Marte, well, he's done. Almost universally these guys are All-Stars and several of them look like Hall of Famers.
This year there are 11 18 year olds (or younger) in A-ball (3 of them were drafted or signed by the Red Sox 

). By the way, it's just 14 at-bats for Vitters. You should be really excited about him.
http://minors.baseball-reference.com/ba ... =&sort=age