We used to consider adolescence ending at age 19, but now scientists in the United Kingdom think we should consider the period of development as lasting from ages 10 to 24.
Adulthood has been pushed back by delayed marriages and parenthood, and young people continuing their education for longer periods of time, scientists have said.
Puberty is biologically defined as the period when the part of the brain known as the "hypothalamus" starts releasing hormones that activate the body's pituitary and gonadal glands.
The report said that while improved health and nutrition had accelerated the onset of puberty in almost all developed countries, greater understanding of continued development had lifted the endpoint well into the 20s. And young people are moving away from their parents, getting married, and having their own children later than at any other point in history.
Dr Jan Macarvish, University of Kent Sociologist told the BBC that the paper's suggestions may may further "infantalise" young people and we should "continue to have the highest possible expectations of the next generation". In the United Kingdom, for example, a girl will now begin her period four years earlier than 150 years ago.
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The average age for a man to enter his first marriage in 2013 was 32.5 years and 30.6 years for women across England and Wales. Body continues to develop beyond the age of 20.
The authors argue that redefining adolescence will help to create more effective policies, such as raising the age at which youth support services can be accessed to 25.
She says delayed partnering, parenting and economic independence means the "semi-dependency" that characterises adolescence has expanded.
A teenager's lifespan has been extended to between ten to 24 years old, from the previous 14 to 19, scientists say. In a 2012 study on the subject, she wrote that inconsistent age definitions only serve to compound the problem of addressing adolescent health concerns.