First sign of being an old fart: The other day at the mall, you were thinking “generation gap” when you saw that young man walking in front of you. Problem is, for you, that “gap” meant the ive inches of fabric between the top of his jeans and the waistband of his drawers. There are things about this world that you don’t understand — things like, Why can’t he pull up his pants? And why didn’t he buy those pants from me?

As a retailer, you try to market to teens and twenty-somethings. But they walk in packs past your door without a glance. It doesn’t make sense. But it will once you read GenBuY: How Tweens, Teens, and Twenty-Somethings are Revolutionizing Retail.

You may have already noticed a dearth of youth in the aisles of mall stores. That’s a problem. And according to Kit Yarrow and Jayne O’Donnell, your “problem” is deeper than you think, because Generation Y (everyone born between 1978 and 2000) is positioned to revolutionize the way shopping is done.

Unlike their parents and grandparents, Gen Yers are confident, the authors say, perhaps because they’ve been doted on by their elders. They’ve never known a world without computers, so they’re “connected” and global. And because they’ve rarely had to wait for anything, they’re easily bored.

So what can you do to attract Generation BuY? First, fully embrace technology; Gen Yers can’t live without it. Recruit a peer champion; it’s better than advertising directly to Gen Y. Keep things new. Engage and inspire.

Using one-on-one interviews, mall visits, surveys, personal observations and expert opinions, Yarrow and O’Donnell (a “consumer psychologist” and reporter, respectively) have pulled together an eye-opening, light but informative marketing atlas for retailers wanting to tap into this emerging group of shoppers.

This tribe of consumers has already unobtrusively (yet not so quietly) changed shopping, almost without the realization of the average Boomer or Gen Xer. Yarrow and O’Donnell provide particularly instructive comparison lists of what teens “needed” in 1978 and what they “need” today.

What they need is a lot of stuff.

And when do they want it? Right now.