Hunters do not produce enough calories to even feed themselves (let alone others) until around age 18

From The Secret of Our Success by Joseph Henrich. Page 63.

Human brain development is related to another unusual feature of our species, our extended childhoods and the emergence of that memorable period called adolescence. Compared to other primates, our gestational and infancy periods (birth to weaning) have shortened while our childhoods have extended and a uniquely human period of adolescence has emerged, prior to full maturity. Childhood is a period of intensive cultural learning, including playing and the practicing of adult roles and skills, during which time our brains reach nearly their adult size while our bodies remain small. Adolescence begins at sexual maturity, after which a growth spurt ensues. During this time, we engage in apprenticeships, as we hone the most complex of adult skills and areas of knowledge, as well as build relationships with peers and look for mates.

The emergence of adolescence and young adulthood has likely been crucial over our evolutionary history, since in hunting and gathering populations, hunters do not produce enough calories to even feed themselves (let alone others) until around age 18 and won’t reach their peak productivity until their late thirties. Interestingly, while hunters reach their peak strength and speed in their twenties, individual hunting success does not peak until around age 40, because success depends more on know-how and refined skills than on physical prowess. By contrast, chimpanzees—who also hunt and gather—can obtain enough calories to sustain themselves immediately after infancy ends, around age 5.5 Consistent with our long period of wiring-up, this pattern and contrast with chimpanzees reveals the degree to which we humans are dependent on learning for our survival as foragers.