DS didn't start speaking words until he was past 24 months, perhaps almost 30 months. We too were worried, especially since DD was speaking clearly at 12 months.

Our wise pediatrician told us there was absolutely nothing to worry about, and said that "when he decides to speak, they will be in full sentences". And that is precisely what happened.

So you should get things checked out, but be aware that there are some late bloomers with regard to speech.