It is an interesting observation, and will be fun for you to follow as language develops further.
I have three kids, and none of them really followed normal pattern for development. We have a very strong family history of late-speaking (relative to other skills), so there seems to be a lot of room during the time frame to pick and choose what they are going to say. We all seem to have waited to speak until we were/are capable of full sentences. I have a sneaking suspicion that children who learn substantially differently from the norm in most other ways are also likely to learn language in an unorthodox manner.
