7 to 8 months
What Your Baby Learns: His fine motor skills improve greatly at this age, and he'll insist on examining anything he can get his hands on, Dr. Ramey says. It will also dawn on him for the first time that words have specific meanings; he'll begin to understand the most common ones he hears.
Keep in Mind: Telling him "no" too many times will hinder his love of exploration. So be sure to put away any dangerous or breakable objects, and make your child's environment as baby-safe as possible.