When my boy is 17 mth, he still cannot say any meanful words but ma ma ma ...
I told my husband that we need to train him up for the 18mth checkup and within 2 weeks, he can say pretty much better e.g. baba (father), meme (mother), paupau (grandma), go go, gaugau (brother) , 包包, 抱抱, 姐姐.
I think it really depends on BB's readiness. It was just an coincidence that he starts to speak meaniful words. However, talks more to him is also important.
Whenever he wants me to hold or ask/give something to me, I'll ask him to call me first i.e. meme before I fulfill his request.
It is quite useful if your BB likes eating and playing, ask him to say some words before giving him the food or plays with him.