Sounds like he's probably still "within normal limits" but on the slow end. The fact that he's trying to communicate is a really good sign.
It could be absolutely nothing (most likely), or it might be the first sign of a problem.
Knowing what I now know, as the parent of a child with special needs, I'd watch carefully, take notes, and bring up your concerns (if you still have them) with his pediatrician at his normal 24-month check-up. What kind of notes?: - Is he making lots of different nonsense sounds? Or just a few sounds over and over. Write down the sounds he does make, and if you can tell, the words he's attempting and how he says them. (For example: cup - 'u) - Do you have any reason to believe his hearing is less-than-perfect? And have you had it checked recently? Any history of ear infections? - Is there any other reason to believe there may be a problem? Has he met all of his other milestones on time? - How are his large- and fine-motor skills? Are you able to compare his skills to other kids his same age? But the most important bit of advice I can give you is simply this: If your gut tells you that there's a problem (not your over-anxious Mom voice - but your gut), then insist on an evaluation by a Speech and Language Pathologist, just to set your mind at ease. | 
