The frontal lobes first kick in at about six months, bringing the first glimmerings of cognition. By the age of one they are gaining control over the drives of the limbic system—if you offer two toys to a child of this age, they will make a choice rather than try to grab both. (Carter, Rita, Ed. Mapping the Mind. CA: University of California Press, 1998, p 22)

In boys the frontal lobes of the brain mature more slowly than in girls. (Gurian, Michael. The Wonder of Boys. NY: Jeremy P. Tarcher/Putnam, 1996, pp 50-51)