The answer: Many of the same retailers who have catered to this group since they were children, growing up with them along the way. Apparel companies are getting ready for the glut of people in their 20s by opening new stores with merchandise that appeals to young adults. According to Philadelphia-based marketing consultancy TWENTYSOMETHING Inc., there are 38 million young people between the ages of 11 and 19 in the U.S.

The CEO of privately owned Metro park, a fashion chain that first opened in 2004 in Glendale, Calif., says he started thinking about new ways to sell apparel five years ago, after watching young consumers and asking himself, "where are all these folks going to go when they get tired of shopping in teenage land?" He wasn't the only one asking that question and coming up with ideas. Abercrombie & Fitch Co. in 2004 started a new store, Reel No. 925, that is aimed at 20-to-35-year-olds. It now has 10 stores nationwide.

Jimmy Z, owned by Aerospatiale Inc, stocks studded denim and blazers with graphics on the back for 18-to-25-year-olds at prices significantly higher than at its flagship chain for teens. In designing its 14 stores -- in places such as Riverside, Calif., Houston and St. Louis -- executives were inspired by the look of a California beach house, with lots of open space and light.

Teen retail giant Pacific Sun wear of California Inc. says it is seeing success with its high-end footwear store for young adults, called One Thousand Steps. And American Eagle Outfitters will launch a new concept this fall with Martin + Rosa, whose target customer ranges in age from 25 to 40. It remains to be seen whether customers will flock to the new chains. The niche is crowded, with retailers such as Banana Republic, Urban Outfitters Inc. and Bebe Stores Inc. already successfully catering to young adults.