Drunken wisdom says that our current generation of young adults is slow to grow up – staying home with mum and dad until well into their twenties.

And this theory of stalled development seems to get a boost from a new paper published in The Lancet by Melbourne researchers.

Professor Susan Sawyer, Director, Centre for Adolescent Health at the Royal Children’s Hospital argues the prevailing age span for adolescence, from 10 to 19, be extended by four years to 24.

The basic argument is that puberty begins earlier – most obviously in girls with the onset of menstruation and other hormonal events – while social markers of adulthood such as financial independence, partnering up and breeding are happening later. (See? Those slackers!)

Some reports about the research have gleefully declared “25 is the new 20.” Others have ruminated on the need for society to “grow up” – which is what the word adolescence actually means. But where a simple reading of the research allows for a fun headline, it misses the complicated point.

Sawyer and her team say that this expansion of adolescence – defined as the phase of life stretching between childhood and adulthood – needs to be taken seriously by law-makers when shaping public policy.

If they do so, it means that the minimum age for voting, drinking and driving would be up for review.

It would also mean that child services paid for by the government would be extended by as much as seven years. Social service groups who advocate for disadvantaged children have been arguing this point for some years.

Bottomline, the catch-all 18 years of age – as adulthood is designated in Australia – would become something more complex and nuanced.

Susan Sawyer told The New Daily that adulthood is Australia was not long ago granted at 21 – and it was only lowered to 18 to justify sending young men of that age off to war. Why not let them drink and enjoy the privileges of adulthood if we expect them to die for queen and country anyway?

A 21st birthday used to mark the onset on adulthood. Photo: Getty

Sawyer’s paper has been misreported as new research. In fact, it brings together a raft of material that has long questioned when adolescence begins and ends – given that the markers of childhood, puberty and adulthood have been in significant a state of flux for at least 150 years. And there is no standard shift among societies.

Since the mid-1880s, the age of menarche (onset of menstruation) has been reduced from 15-16 to 11-12 in early industrialised countries such as the UK. This largely due to improved nutrition and childhood health.

But these changes are occurring more quickly in newly industrialised countries, writes Sawyer. “In China, the mean age of menarche has reduced by four and a half months per decade in the past 25 years.’”

And there’s much that isn’t known. Human beings are slow-maturing animals and a full understanding of that maturation – most notably the link between a late-developing brain and a young person’s ability to moderate behaviour through reasoned choices – hasn’t yet been gleaned.

A 2009 paper in the Journal of Adolescent Health noted that longitudinal neuroimaging studies demonstrate that the adolescent brain continues to mature well into the 20s – but evidence for links between brain development and “adolescent real-world behaviour remains sparse”.

The paper also that adolescent brain development research “is already shaping public policy debates about when individuals should be considered mature for policy purposes”.

Susan Sawyer argues that the terms of that debate be broadened, given that adolescence – the path from childhood to adulthood – “now occupies a greater portion of the life course than ever before”.

She says that this expanded adolescence comes at a time “when unprecedented social forces, including marketing and digital media, are affecting health and wellbeing across these years”.