No need to worry. My daughter, now 16 months and 1 week old, can only say "ba-ba". Even when she want to get her toys or have buscuits, she still doesn't speak a word and just "ah-ah-ah" and even scream.
I've asked my friends and elder relatives, they are of the opinion that different babies have different pace in development, 16-months old babies cannot speak is not a problem. We have to wait till 2 years old to assess the baby further.