G.G.
2 of my best friends have children who are one month apart (now 19 and 20 months) and neither of these kids says more than 5 words. Their development is normal, but they just don't talk much. My daughter was speaking in full sentences at the same age (which is great, until they won't be quiet!) The point is, every kid is different and as long as you see signs that your child understands you, I would not be worried about this.