Viewpoint
The age of adolescence

https://doi.org/10.1016/S2352-4642(18)30022-1Get rights and content

Summary

Adolescence is the phase of life stretching between childhood and adulthood, and its definition has long posed a conundrum. Adolescence encompasses elements of biological growth and major social role transitions, both of which have changed in the past century. Earlier puberty has accelerated the onset of adolescence in nearly all populations, while understanding of continued growth has lifted its endpoint age well into the 20s. In parallel, delayed timing of role transitions, including completion of education, marriage, and parenthood, continue to shift popular perceptions of when adulthood begins. Arguably, the transition period from childhood to adulthood now occupies a greater portion of the life course than ever before at a time when unprecedented social forces, including marketing and digital media, are affecting health and wellbeing across these years. An expanded and more inclusive definition of adolescence is essential for developmentally appropriate framing of laws, social policies, and service systems. Rather than age 10–19 years, a definition of 10–24 years corresponds more closely to adolescent growth and popular understandings of this life phase and would facilitate extended investments across a broader range of settings.

Introduction

The word adolescence derives from the Latin adolescere—to grow up. However, defining the phase of life that stretches between childhood and adulthood has long posed a conundrum. At the start of the 20th century, G Stanley Hall loosely defined adolescence as the developmental period ranging from age 14 to 24 years in his treatise on adolescence.1 More than 50 years ago, WHO proposed that adolescence spanned from 10 to 20 years of age, noting that although it commenced with puberty, the endpoint was less well defined.2, 3 The UN Convention on the Rights of the Child defines a child as an individual aged 0–18 years and, in time, the UN has come to formally define adolescence as the period between 10 and 19 years of age.4 Across different countries, cultures, and contexts this definition continues to be met with surprise, both about when adolescence starts (the notion that a 10-year-old person is a child, not an adolescent) and when it ends (the belief that a 19-year-old person is already an adult).

Overlapping with adolescence, the term youth became popular about the time of the UN's first International Youth Year, in 1985. Although youth is now typically defined as the period between 15 and 24 years of age, the Barcelona Statement from the associated world congress defined youth as a social category, and the congress proceedings were remarkable because of the absence of age definitions.5 Most definitions of the more recently introduced terms young adulthood and emerging adulthood range from about 18 to 26 years of age.6, 7, 8 Given such variation, it is no wonder that the more generic term young people is so often used without definition.

Another challenge is raised by the non-mutually exclusive definitions for the developmental years, particularly adolescence, in which a 16-year-old individual is a child, adolescent, and youth at the same time (figure 1).9 These words convey very different meanings: child suggests dependency, youth signals independence, and adolescence captures the notion of the growing individual who is able to take increasing responsibility, but who still needs more protection than an adult.

This Viewpoint outlines the extent to which the patterns of biological growth and social role transitions that define adolescence have changed over time. We aimed to consider how well the current definition of adolescence aligns with contemporary patterns of adolescent growth and popular understandings of this life phase, because how we conceptualise and define this life phase influences the scope and focus of laws, policies, and programmes intended to protect and empower adolescents.

Section snippets

Distinct phase of biological maturation

Homo sapiens evolved as a slow-maturing species with distinct growth phases, including a long period of dependency in infancy, an extended period of childhood growth, and a prepubertal juvenile phase followed by a delayed puberty.10, 11 The activation of the neuroendocrine hypothalamic–pituitary–gonadal axis has long been considered the biological event that marks the start of both puberty and adolescence, but patterns of growth have changed over time. Puberty now starts earlier, a change

Social role transitions

Historically, the end of adolescence was largely defined by social role transitions, especially those around marriage and parenting. In the USA, the median age of marriage reached a nadir in the 1960s of 22 years for white men and 19 years for white women.27 Since that time, the age of marriage has substantially risen in all but the poorest countries. In China, for example, the mean age of first marriage for women increased from 20·2 years in 1970 to 23·9 years in 2010, as did the mean age of

Great expectations

The upwards extension of the timing of role transitions to adulthood has been followed by shifts in the social environments in which adolescents are maturing. The social world in which adolescents are growing up is more urbanised, mobile, and globally networked than ever before. Notwithstanding the benefits of socially connecting with peers, peer influences are increasingly amplified by social media and exploited by industry in ways that undermine health and wellbeing. These powerful influences

Naming the age of transformation

The new era of the Sustainable Development Goals and the Global Strategy for Women's, Children's and Adolescents' Health provides a timely opportunity to seriously tackle the challenge of implementing multisectoral investments for adolescents.4, 45, 46 Given the increasing demands on adults in the workplace and family life, there is every reason to maximise investment across the transition from childhood to adulthood, which has been shown to yield substantial economic, social, and health

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