Hi K.,
I've been through this myself. I am the mother of 5 children and my youngest son (#4 in the lineup) refused to talk at that age as well. He has 2 uncle's that were born deaf so of course that is the first thing that I thought of. We put him through several intensive tests for his hearing, all of which came back that he had very good hearing. It used to drive me insane that he wouldn't even use the simplest words. I did a lot of reading on the subject and talked to his pediatrician, a psychologist at church and any other professional that I could think of. All of them told me the same thing, "He'll talk when he's ready." They also asked me to look at all the things in his life that were controlled by other people, and that perhaps his not talking was his way of having some kind of control over something.
I did listen to all they were saying, but having had 3 older chhildren that talked, a LOT I should add, it still didn't seem normal to me that he didn't talk. I worried about it, I tried everything under the sun to get him to talk and finally I just gave up.
A few weeks after I gave up trying to get him to talk he began saying little words, "yes" "no" "ok" but that was about it, always just 1 word.
Just before his 4th birthday, we were driving to my parents house, about 4 hours from home. For once the other 3 kids were being pretty quiet, playing with game boys or coloring while I drove. All of a sudden, from the back of the van I hear a little voice say, "The moon is 2 million miles from the earth." I asked him how he knew that and he said, "Nova" (his favorite show). At that point he began telling me all about the moon, then volcano's, then anything else he could think of to tell me that he'd learned from Nova. I thought the kid would never stop talking!
He starts the 5th grade this year, he's in a class for "gifted" children and doing just fine. And, over the years I have wished a thousand times that I'd never pushed him to start because talking soon became the thing that got him in trouble as he was eager to share all the things he knew with anyone willing to listen, and it really got annoying.
My point is, all this time that I was worried that he wasn't talking he'd been learning a skill some people NEVER learn. He'd been learing to LISTEN. So, maybe the fact that the little boy your referring to isn't talking yet isn't really something to be so concerned over.