It's a trend changing the complexion of households across the Western world: young people are lingering much longer in the family home.
Across the 35 wealthy member nations of the Organisation for Economic Cooperation and Development, almost 60 per cent of those aged 15-29 are still living with their parents.
In Italy, Slovenia and Greece more than three quarters of that age cohort have not yet flown the coop. Portugal (75 per cent), Spain (74 per cent), Hungary (74 per cent) and Czech Republic (70 per cent) are not far behind. Australia's proportion has reached 54 per cent.
There's been a marked change in the “life course transition” to independent adulthood in most advanced economies over the past 20 years.
The average age at which women in OECD countries have their first child rose by almost three years to 28.7 years between 1995 and 2014.
The average age at first marriage for both men and women in the OECD has climbed from the mid-20s into the low to mid-30s since 1990.
Local cultural norms play a role of course. But so does economics. Since the 2008 global financial crisis the proportion of young people living with their parents has climbed across the OECD.
In France the share spiked by 12.5 percentage points in that period. Most nations with a high proportion of under-30s still living at home also have a very high rate of youth unemployment.
Australia's share of under-30s living with their parents is a little lower than the OECD average but it has risen sharply in the past few decades despite our relatively strong economic performance.
In the 1970s only about one in five under-30s in Australia lived with their parents but now it's one in two. The rate of increase has been especially rapid since the early 2000s.
There's a mix of factors at work. One driver is education. Young adults are spending far more time studying for post-school qualifications than in the past and staying at home while they do it.
This investment in know how promises to pay economic dividends in the long-run. For some young adults, staying in the family home is a lifestyle choice. It can free up funds for travel or cater for preferences like being near the beach or close to work.
The latest figures show that a higher proportion of twenty-something men live with mum and dad than their female counterparts.
But Professor Ariadne Vromen, an expert in youth and politics at Sydney University, warns these trends suggest the transition to independent adulthood in Australia is getting harder.
And that raises questions about how well society is functioning.
"I think that a majority of people under 30 still living at home is a problem," she said. "It tells us something about the difficulties that young people face in gaining financial independence by moving out of home."
The high cost of housing in some Australian cities is an obvious contributor. The casual modes of employment encountered by many younger workers may also be a factor.
The international trends highlighted by the OECD suggests the proportion of Australian twentysomethings living at home could rise even further.
But is it healthy?