He's actually 17 months if we want to get specific. On his 1st birthday, I managed to get him to answer the question "X, how old are you?" with "Wah!", which only became an articulate "One!" around Christmas/16 months, which was also about the time he started being able to say 1 to 10.
He actually is a pretty amazing kid. He's miles ahead of other kids his age, even some who are older. I wasn't expecting to be able to teach him counting until next year, so I'm being very relaxed about it right now and making it fun. He's 1, not 5, as far as I'm concerned, he can do what he wants, but if he's into it, I'll teach him.
Consider P₁ ∈ H and P₂ ∈ G where H is the set of HN posters, and G is the set of persons in the general population. Let p(P U) be the probability that a person, P, will produce an utterance, U, using mathematical terms and/or notation. Let q(U) be the probability that U will be better understood in mathematical terms than in plain language.
That's extremely amazing for a kid that is exactly one years old, rather than, say, 1.x years old for high values of x.