Homo sapiens is unique in having four prolonged and pronounced postnatal pre-adult life-history stages: infancy, which lasts for 30-36 months, and ends with weaning from breast feeding in traditional societies; childhood, which lasts for additional 2-4 years, and concludes in a degree of independence for protection and food provision; a juvenile stage of 3-4 years that terminates with the readiness for a sexual maturation process; and adolescence, which lasts for 3-5 years, and culminates in fertility.
With regard to juvenility, this implies two transitional periods that only humans have: a transition from childhood to juvenility and from juvenility to adolescence. Juvenility "the age of reason and responsibility" and concrete operation is also the elementary school age, and offers opportunities to prepare for the social complexity of adolescence.
Here I define the transition to juvenility by three variables: adrenarche - the onset of adrenal androgen generation, growth pattern - decelerating from a linear childhood growth velocity, and adiposity rebound acceleration of body mass index. The data presented suggest that this period is endowed with programming/predictive adaptive response of body composition to the environment.