From what I have read, receptive language skills are a large indicator of whether or not a child is a late bloomer or delayed. From what you have indicated, his receptive language seems right on (but I am no expert).
FWIW, there is something called the Einstein syndrome, brilliant childen speaking later, as in first sentence at 3.5 or 4 yrs. If your physician has not indicated a problem (hearing, tongue, hard or soft palate), he may just be within normal range. http://kelleyward.hubpages.com/hub/Children-Who-Talk-Late
Also 'words' are counted as anything that is repeated to indicate the same thing, dodo for dog, pa for hat and so on, so long as it is the same.
My son was only saying first syllables at 23 months and within two weeks the words were spilling out like a waterfall. WIthin 3 days, sentences of 3-5 words. It was astounding. I never would have predicted it.
He skipped the 'dog yard' 'water cup' phase and went right into real sentences and conversations, it was amazing to say the least. But that is just an anecdote, what matters is your child and his development. If you have concerns, I would address them. Not because of what the neighbor, the well meaning relative, or anyone else says, but because of what you feel or your instinct is telling you.
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