Girls’ brains mature earlier than boys’. Myelination continues in all brains into the early twenties, but in young women it is complete earlier than in young men. (Gurian, Michael, PhD, and Patricia Henley, with Terry Trueman. Boys and Girls Learn Differently! p 18-26. CA: Jossey-Bass, 2001.)

Myelination in the spine occurs from top to bottom. Therefore, it is completed in the mouth, hand, and arms, before it is adequately completed in the legs and feet. (Healy, Jane M., PhD. Your Child’s Growing Mind. p 31-32. NY: Doubleday, 1987, 1989.)

The final layer of myelin is not completed until the mid-twenties.(Greenfield, Susan, Con. Ed. Brain Power. p 157. Britain: Element Books Limited, 1999.)

The reticular formation (e.g., maintaining attention), usually only becomes fully myelinated at or after puberty, which is why prepubescent children have a short attention span. The frontal lobes do not become fully myelinated until full adulthood. (Carter, Rita, Ed. Mapping the Mind. p 20. CA: University of California Press, 1998.)