Allayna is beginning to reach some very important developmental milestones in her language development, and her parents are excited to witness her progress. Most notably, Allayna is asking questions and becoming an active participant in conversations. In fact, she has a vocabulary of nearly 900 words at this point and her parents report that they love hearing her tell stories about her day. Considering that Allayna is on a typical language developmental trajectory, what is her approximate age? How do you know? .