D. C. Phillips (2014). Encyclopedia of Educational Theory and Philosophy. SAGE Publications. pp. 18–19. ISBN978-1-4833-6475-9. „On average, the onset of puberty is about 18 months earlier for girls (usually starting around the age of 10 or 11 and lasting until they are 15 to 17) than for boys (who usually begin puberty at about the age of 11 to 12 and complete it by the age of 16 to 17, on average).“