Adolescence as a separate stage of development was?

A relatively recent social construction.

Adolescence as a separate stage of development is a relatively recent social construction. The concept of adolescence did not exist in most cultures until the late 19th century. Before this time, children were considered to be adults as soon as they were able to work and marry. The idea of adolescence as a time of transition between childhood and adulthood is a product of industrialization and the rise of mass education.