Almost 18 months old.
Now separating rocks into two's and counting 1 to 10, although 9 seems to always be amiss.
We are continually amazed at how a young mind, when left alone, learns!
That said, I still struggle with unschooling him or having a set curriculum when he turns 3. I am very tempted to get the Core Knowledge Preschool book and activity books (1 and 2) at the moment!