lifestages

Life stages refer to the phases through which a living organism or a person progresses as it develops, typically marked by distinct biological, psychological, or social characteristics. The concept helps organize understanding of growth, change, and aging across disciplines such as biology, psychology, sociology, and demography. In biology, life stages can be discrete transitions such as metamorphic cycles (for example, egg, larva, pupa, and adult in insects) or stages in plant development (seed, germination, vegetative growth, reproduction). Not all species show clear boundaries, but the idea remains a useful framework for describing development over time.

In humans, life stages are commonly used to segment birth to death into periods with relatively shared experiences and needs. Conventional divisions include prenatal, infancy (roughly 0–2 years), early childhood (2–5 years), middle childhood (6–11 years), adolescence (roughly 12–18 years), early adulthood (18–40 years), middle adulthood (40–65 years), and older adulthood (65 years and up). The exact ages and labels vary by culture, policy, and scholarly tradition, and there is substantial individual variation within each stage.

Life stages are used in research, education, health care, marketing, and policy to study developmental milestones, allocate resources, and tailor interventions. They are a pragmatic, though simplifying, tool for understanding growth and change, with the caveat that boundaries are approximate and culturally contingent.