Although waving hello and bye-bye seems like just a fun thing to teach your baby, it is actually an important developmental milestone. Most experts think that it can be an early sign of autism or another developmental disorder if your child isn't making any gestures by the time he is twelve months old. These gestures include waving, pointing, and reaching for things.
Keep in mind that most babies can wave once they are seven to 14 months old.
Sources:
Functional developmental evaluation. Prerequisite to habilitation. Capute AJ - Pediatr Clin North Am - 01-FEB-1973; 20(1): 3-26
Linguistic and auditory milestones during the first two years of life: a language inventory for the practitioner. Capute AJ - Clin Pediatr (Phila) - 01-NOV-1978; 17(11): 847-53
Clinical linguistic and auditory milestone scale: prediction of cognition in infancy. Capute AJ - Dev Med Child Neurol - 01-DEC-1986; 28(6): 762-71
The Denver Developmental Assessment (Denver II)
