Eliminate the ranges one by one. Birth to 2 years is infancy, when basic motor and language skills first appear. 3 to 5 years is early childhood, the preschool stage. 6 to 11 years is late childhood, the primary school stage marked by steady growth before puberty. That leaves 12 to 15 years, the stage where puberty begins and physical, emotional and social changes mark the shift from childhood to adulthood, which is exactly what developmentalists label adolescence. \[\boxed{12 - 15 \text{ Years}}\]