What makes an adult an adult?
Is there a pre-defined age? Say, when you turn 18 and are officially "legal". Or can you only pass after you've checked off a certain number of pre-selected rites of passage? The mortgage, the marriage, the 9-to-5 job, 2.5 kids, Volvo Hatchback, and white picket fence, etcetera.
Well, science has an answer and the truth appears to be less clear cut. The latest research seems to suggest that we don't become fully formed adults until we reach our thirties – though as with puberty, wisdom teeth, and losing our virginity, the exact age varies from person to person.
The reason scientists have identified our thirties as the entry point to adulthood is due to the extent of changes, particularly in the brain, that takes place in our late teens and throughout our twenties. For example, our neurons continue to develop, connect, and become more refined in our third decade, even if the bulk of the change took place in our mid-teens. (And it can continue to change well past our thirtieth birthday.)
These changes can affect our behavior and even our propensity to develop mental health conditions like schizophrenia. To take the example of schizophrenia, the average age of onset is late teens to early twenties in men and late twenties to early thirties in women.
"What we're really saying is that to have a definition of when you move from childhood to adulthood looks increasingly absurd," Peter Jones, a professor of neuroscience from Cambridge University, told reporters at the Academy of Medical Sciences in Oxford, UK.
"It's a much more nuanced transition that takes place over three decades."
This idea that childhood stops at 18 has been gaining a lot of traction recently, with an article published in the Lancet Child & Adolescent Health journal just last year arguing that the period of life we call adolescence lasts much longer than most of us realize.
The term "adolescence" was first described in a 1904 paper published by the psychologist G. Stanley Hall called "Adolescence". She defined the word as "the phase of life stretching between childhood and adulthood". Most of us associate this phase with the teen years but it can start as young as 10, researchers say, when some girls start to hit puberty.
It continues, they explain, "well into the twenties" as the body and brain continues to develop and socio-economic forces (think: the rising cost of housing, an unstable job market, and student debts) delay the traditional signposts of adulthood (partnering, parenting, and economic independence) and extend the period of "semi-dependency" that is adolescence.
Similarly, recent neuroscience research suggests putting a timestamp on adulthood (18 years plus) is an old-fashioned way of looking at things.
"There isn’t a childhood and then an adulthood," Jones explained. "People are on a pathway, they’re on a trajectory."