I normally don't comment on posts, but I do have a Masters in Language Acquisition and currently writing my defense for a PhD in Human Development so this comment sucked me in... Developmentally speaking, you change the most over the course of your first 24 months of life (or 2 years). It is standard practice to reference age in months for children under 3 because 4 months is actually a very significant amount of time during this period of life, especially in terms of language development (which this post is specifically referencing). If this child were older than 2, it would make sense to start speaking in terms of half years. If they were younger than 3 months, we would be stating their age in weeks.
Its smaller, easier, and way more understanding.
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