The news is bad. For parents at least.
New research says young people don't mature until 24.
Not until 24. That's about four years later than we thought.
Here is what Professor Susan Sawyer and colleagues wrote about adolescence last week in established British medical journal: The Lancet.
''The shape of adolescence is rapidly changing - the age of onset of puberty is decreasing and the age at which mature social roles are achieved is rising.'' And it's engrossing that medical science has finally caught up with social science - because those of us who read sociologists know that the idea of the ''kidult'' has been around for years.
What kidult really means is that there is a long time between when you feel that first rush of wanting to bonk someone and getting a job that might pay you enough so you can set up house (and bonk someone on a regular and enjoyable basis without having to share a house or bathroom).
The word kidult itself is offensive. No one who is 20 will embrace - or see anything in common - with the word kid. A 20-year-old is not a kid. But the concept is one that we as parents need to accommodate.
How do we deal with the fact that these young people look like adults: as big as we are; with (usually) a more active sex life; with wants and needs that fit with fully-formed adult wants and needs; with aspirations and hopes? And how do we all live in the same house?
And here is where I confess my own failings as a parent. Or some at least. We don't have all day.
As soon as my kids became teenagers, I talked obsessively about moving out. I explained that we both (their parents) moved out of home when they were 18 (this is true, although it was somewhat easier to get financial aid in the form of a tertiary education allowance scheme). I said that it was important to be financially independent and that the ability to support yourself led to increased maturity.
And when they got to the age where they should have moved out of home, I began to remove maternal support mechanisms. As in instant laundry; dinners in the fridge ready for the microwave; packed lunches; breakfast smorgasbords; lifts to everywhere. And the odd cash handout.
While we still do that for our children depending on individual needs (I don't think I could ever have rustled up two grand for a rental bond without asking my parents for help), it is not automatic. I now try to spend most of the money I earn on myself. I consider it to be my turn.
But if I'd read the material in The Lancet 10 years ago, I would not have been so quick to push the kids out of the nest. And here's why. Although I am a reasonably permissive parent (according to my friends), I'm not mad.
Here are what I consider to be the ground rules on advice for parents with young adults still at home.
Sex, for instance, in most cases, doesn't kill you. You appear to still be alive despite your massive mortgage. Tell your children to have as much of it as they like although remember to eat and do other forms of exercise; of course you can do it at home, just don't keep me awake. Tell them to make sure they practise safe sex. I don't just mean keep away STDs. If their brains are still developing, do they really think they are old enough to be a parent? Plus, if you have to support them, can you manage the next generation as well?
Drugs and alcohol? Well, they can kill you. And US researchers showed last year that heavy drinking during teenage years can affect the development of the brain.
Money? It's important to have paid work, no matter how independently wealthy you are. Don't be a bunny bank.
Eating. Remind them to do it. Regularly. Not just Red Bull and Mars Bars. And here is an area to which young adults living at home can contribute. If they can't cook, it's your fault so buy them The Naked Chef. Not just because of the title.
And if your kids are at home as they develop into mature adults, you can still have discussions about these things because you are there to witness what they do. It's not like you can tell them in the ranty way you did when they were 10 (oh yes, I'm sure some of you perfect parents don't rant) - but there are ways to greet a morning hangover where disapproval can be implicit yet helpful. At least from the point of view of the disapprover.
The newest research shows that in an Australian setting, introducing your children to the European method of drinking wine at a young age, doesn't work. It can even be harmful because the age at the time of drinking onset determines, somehow, what happens next.
I'm actually sorry I encouraged my children to leave home. Not because I miss them. I don't.
But I do miss the opportunity to tell them every day that I love them. And to nag them a little.
Actually, I lie. I miss the opportunity to nag them a lot.