The idea that human lives follow a progression of stages, with different impulses and challenges appropriate to each, is deeply embedded in many cultures. Stages are enumerated in Hinduism and in Native American traditions. When Shakespeare wrote Jacques’s celebrated “seven ages of man” speech in As You Like It (“At first the infant / Mewling and puking in the nurse’s arms …”), he was elaborating on an idea familiar to his audience.
Studying the question from a scientific rather than a poetic perspective, adult development theory has taken two approaches. One group of theories focuses on an age or phase in the life cycle marked by certain characteristics, ways of being, or issues one faces (Erikson, ...