The storybook character Peter Pan may have escaped the fate, but in the real world growing up is inevitable. Biologically speaking, the turn to adulthood happens in humans when the brain tells the pituitary glands to start producing hormones, jump-starting puberty. This typically happens around age 10 in girls and 11 in boys. But, for a small percentage of children, the process can start much earlier. If the brain initiates the process before age 8 in girls or 9 in boys, the child experiences central precocious (or “early”) puberty.