My son was saying 20 words by the age of 18 months and by 2 1/2 had over a hundred words, however they were nearly all labels, he found it very difficult (and still does to a certain extent) to structure sentances, ask questions etc etc. By 3 years old he was quite echolaic, confused me, you, your etc rearely used the word no and never said yes in response to a question.