Difficult to answer I think. DD has been making sounds that are like words since about 9/10 months, but it's only been recently (14mo) that we've been convinced as she is using them often and consistently.
DD was talking in full sentences at 18 months, ds is 18 months now and only says a few words, mummy, daddy, Ollillia (Olivia) hello, bye,dog and roar! he is starting to say new things every day now though. They are all different
Coming from a slightly different angle, I remember reading that the normal range of vocabulary for a 2yo was anything between 5 and 500 words - so I guess a child could be pretty close to 2 with no words and be in the normal range.