Billboard's 21 Hottest Music Stars Under the Age of 21

Billboard.comhas put out their annual list of "The 21 Hottest Music Stars Under the Age of 21".  They didn't really reveal the criteria they used to rank these kids . . . but they did do write-ups on "what makes them hot."

-Here's the list, along with their ages . . .

1.)  Justin Bieber, 17  (--He was #2 last year.)

2.)  Tyler, the Creator, 20

3.)  Selena Gomez, 19  (--She was #3 last year.)

4.)  "American Idol" winner Scotty McCreery, 17

5.)  "America's Got Talent" star Jackie Evancho, 11

6.)  Rapper Mac Miller, 19

7.)  Demi Lovato, 19  (--She was #8 last year.)

8.)  Nick Jonas, 19  (--He was #6 last year.)

9.)  Female rapper / dancer Rye Rye, 20

10.)  Nickelodeon star Victoria Justice, 18

11.)  Rap producer Lex Luger, 20  (--He was #11 last year.)

12.)  The Italian opera trio Il Volo . . . they're 18, 16 and 16.

13.)  Cody Simpson, 14  (--He was #20 last year.)

14.)  Willow Smith, 10  (--She was #7 last year.)

15.)  Greyson Chance, 14  (--He was #9 last year.)

16.)  The R&B group Mindless Behavior . . . all four of them are 14.

17.)  South Korean pop singer HyunA, 19

18.)  DJPorter Robinson, 19

19.)  The British boy band One Direction, they're 19, 18, 18, 18 and 17.

20.)  Puerto Rican reggaeton singer Miguelito, 12

21.)  Miley Cyrus, 18  (--She was #10 last year.)

(--If you don't mind awkward slideshows, you can browse through "Billboard's" write-ups on each kid, beginning here.)

(--12 kids from last year's list didn't make the cut this year.  Six of them are apparently no longer "hot" . . . while the other six are now too old to qualify.  That includes last year's #1, TAYLOR SWIFT.  She's 21 now.)