Ming from Agents of Speech argues that 18 months is not too young for therapy. At this age, children typically use single words like 'mama' or 'dada' consistently to reference real concepts. A word is any sound a child uses the same way across different settings.
When parents go to pediatricians, the doctors will say we wait and see because it's only 18 months old. That aside, the wait and see part, if you look at speech and language developmental milestones across different countries and cultures, 18 months should be where children start to use single words. They should start to use at least a word or something that reflects something in the real world. So it could be Mommy, it could be dad, it could be Mama, it could be whatever. As long as the word references something in the real world and your child is using that in the correct way, that's counted as a word. What's counted a word? What not. As long as the use of a speech sound correlates to a concept in the world that is always consistent and using the same over and over again, and if the child uses that same sound or word in different settings for different things, then that's still a word.
