My twins are 18 months old. DD talks a LOT and has a really big vocabulary and is ver verbal for her age. DS does not speak at all. He has a few words he tries out like "hi" and... thats about it. He does communicate through some signs and gesturing and grunting. He makes a lot of sound effects and will make the dominant consanant sound of a word. Like he'll make a "tss" hissing sound to say sister. If you ask him a question he will sometimes respond appropriateky, sometimes just ignore you. I'm not specifically worried because he is the only boy with 3 very talkative sisters, but it starting to tug at the back of my brain a bit. He had some oxygen/lung issues at birth and we dont know if there were any repercussions from it neurologically.