have two dd, age 6 and 2, don't worry about when they start talking, they all do it differently, worry about if they will ever shut up, once they start. It has been a constant stream for about five years and now in stereo for the last year.
My DS1 started speaking a bit late and DS2 has really only just started at 16 months. He said the odd word now and then but then didnt bother for a few months and now EVERYTHING is (pointing) 'cat cat'. I wasnt really worried because I had it with my 1st too. I read somewhere that 2nds+ can be slow talkers as they have another child to do the talking for them ...which I think def explains mine. I wouldnt worry unless your HV is.