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After this chapter, you should be able to:

• Explain the changes in physical growth and brain growth
• Compare and contrast different male and female changes that occur during puberty
• Discuss teenage pregnancy, birth control, and sexual health
• Summarize adolescent health: sleep, diet, and exercise
• Explain the prevalence, risk factors, and consequences of adolescent pregnancy and sexual health
• Describe factors contributing to increased mental health issues for adolescence
• Identify symptoms and treatment approaches associated with select mental health disorders

Adolescence is often defined as the period that begins with puberty and ends with the transition to adulthood. The commonly accepted beginning age for this period of development is age 12. When adolescence ends is harder to pin down. When does adulthood truly begin? Are we an adult at 18 years of age? Or 20? Or even older?

Adolescence physical development has evolved historically, with evidence indicating that this stage is lengthening as individuals start puberty earlier and transition to adulthood later than in the past. Puberty today begins, on average, at age 10–11 years for biological females and 11–12 years for biological males. This average age of onset has decreased gradually over time since the 19th century by 3– 4 months per decade, which has been attributed to a range of factors including better nutrition, obesity, increased father absence, and other environmental factors (Steinberg, 2013).

Completion of formal education, financial independence from parents, marriage, and parenthood have all been markers of the end of adolescence and beginning of adulthood, and all of these transitions happen, on average, later now than in the past.^[1]