One Direction: 21 Under 21 (2012)
No. 2: One Direction
Birthdates: Zayn Malik - Jan. 12th, 1993 (age 19); Harry Styles - Feb. 1, 1994 (age 18); Louis Tomlinson - Dec. 24, 1991 (age 20); Niall Horan - Sept. 13, 1993 (age 19); Liam Payne - Aug. 29, 1993 (age 19)
Why They're Hot: This time last year, One Direction was a U.K. phenomenon that had yet to make a blip on this side of the pond. A lot has changed in 12 months. In March 2012, 1D saw the U.S. release of their debut album "Up All Night" and became the first British group in history to bow at no. 1 on the U.S. Billboard charts with their debut album. Since then, the only direction the fresh-faced quintet has gone is up. The group has sold more 12 million albums worldwide ("Up All Night" is currently the 2nd biggest selling album of the year in the U.S.), they owned the 2012 MTV VMAs (winning 3 trophies, including the coveted Best new Artist award), and the announcement of their second album "Take Me Home" (which drops in November 2012) was met with squeals of delight around the globe. 1D's massive 2013 world tour was an immediate sell out and includes a headlining gig at New York's Madison Square Garden, plus a 7-night stand at London's 02 Arena. By this time next year, One Direction may very well be in sync with some of the biggest boy bands of all time.
Video Below: One Direction's "Live While We're Young"