I'm worried something bad happened to him?

a 28 year old specialist in Iraq"
"I've been told he probably was busy with something army-related"
Sounds like working for a private military army contractor (Blackwater, now Ex or Dyncorp, PAE and the like) (they have about as many soldiers in Iraq and Afghanistan as the US army. link link
The correct word might be "mercenary".
"So what should I do?"
If he were in the regular US army, you'd maybe get news from the Army if something went wrong and if he gave your address.

IDK if the private military contractors are that thoughtful.

Wait and see: he might be on some mission, with no possibility to communicate.
Don't loose hope!

You asked the question and you already answered it.. just wait and see if he's okay in few days..

but I gotta ask you something.. is it okay to date a 28 year old guy?
arent you considered a minor?

thats illegal ! Perhaps you should talk about it with a member of your family who is old and wiser. You don't wanna be taken advantage of ,do you?
Usually those guys are just after young gurl to pop them., so be carefull and talk about this with someone.

Worry about yourself rather than worrying about him.. he is fine!