Why my baby won't sign any time soon

In sign language class yesterday one of the moms asked why her six month old baby wasn't signing back to her yet. And the nice instructor said not to expect any signs til 9 months at the very earliest, and that twelve months was more common. She also said girls usually will sign back sooner, because girls are more interested in communicating with people, while boys are more interested in doing THIS:






Dear Lord, help us - the baby is climbing the stairs...