They are young at heart, their pockets are deep and advertisers want to get inside their heads.
Meet the 'grups' - in their 30s and 40s, they act more like 20-somethings, but with plenty more cash. They have been credited with killing off the generation gap as they redefine age and as their ranks swell, advertisers are zoning in.
They want to know what makes this Peter Pan demo-graphic tick - people like Londoner Lee Wheatley who regularly bounds across a stage, belting out tunes for his band "Senator Bear".
The 36-year-old photography director with a passion for guitars and trainers, has much more spare cash than he did in his 20s and his enthusiasm for bands and bars shows no sign of waning.
"I can never see myself with a side parting, a suit and saying 'hello darling, how's your day been' as I come home to my wife every night. That's so kind of alien to me," said Wheatley.
"In this generation the last thing you want to be is what your dad used to be. Even though I've got a kid, I've got an almost pathological stubbornness against changing my lifestyle."
The term 'grup' was coined in a New York magazine article, and comes from a Star Trek episode featuring a planet run by wild children trapped in perpetual youth. The children call Captain Kirk and his crew grups, short for grown-ups.
Rarely seen in pin-striped suits, grups of either sex can easily be spotted in discreetly branded battered jeans, Tshirts and old-school trainers, while blasting the latest Raconteurs or Flaming Lips tracks through permanently attached iPods.
For this demographic, work-life balance is often more important than a middle management job and company car.
"People don't think they're bucking any sort of trend by still going clubbing when they're 35 or 36 and wearing Converse trainers. Every-thing's much more fluid," said Laura Simpson, manager of ad agency McCann Erickson's Pulse UK consumer insight division.
"There's a broader movement in society towards staying youthful for longer, it's a trend our clients are certainly aware of."
Grups' favourite activities might include going to see an unsigned guitar band, hanging out in hip bars and the occasional club, maybe jetting off to India or Brazil for a few weeks' summer sun and heading to the slopes to snowboard each winter.
"The crucial difference these days is that the older generation aren't consuming to appear younger, they just aren't growing old like their parents," said Dylan Jones, editor of GQ magazine.
"We are already seeing 60-something men who buy the same clothes, listen to same records, see the same films and browse the Web in exactly the same way as 20-somethings."
Advertisers are now relying on "psychographics" which concentrate on consumer attitudes and values rather than age groups as they promote products that may now appeal equally to grups in their 40s and to teenagers.
Jason Lonsdale, senior planner at advertising agency Leo Burnett, says advertisers need to work their way into the mindset of this media savvy group who shun brash status symbols, and concentrate instead on subtly building brands. "It's the opposite of footballer fashion. The £200 jeans wealthy 30-somethings might buy in this mindset will be incredibly discreet, they won't be Dolce & Gabbana with rhinestones all over," said Lonsdale.
The New Zealander, who confesses to fitting the grup criteria himself, says brands such as New York's Rogan jeans, California's Trovata clothing or Spain's Camper shoes use authenticity to tap into the grup psyche.
Rather than tragically clinging to outgrown notions of youth, grups are seen as defining it in their own terms.