Michelle Wie (25).

I'll give my top 3:

Bella Thorne-Actress, Age 17 (18 in Oct).
Victoria Justice-Actress, Age 21.
Taylor Momsen-Singer, Age 21.

Let's see if I can gracefully dance through this minefield and appease both parties.  Wish me luck...

My vote is - Saeko Busujima from High School of the Dead.  She's young, beautiful, mysterious, honorable, the purple haired President of the Kendo Club, is completely unafraid of the living dead, and rocks a katana like a woman possessed.  In other words - a complete badass in a serafuku.

Even though I have no idea how old she is (she is in high school, well - until the world ends, anyway) but here's the disclaimer - she's a anime character.  So hopefully no one will take any offense at that.  And if you do, please seek therapy immediately as it's a FRICKIN' CARTOON!  LOL

Well, there may be one group I did offend (hopefully not) - TER admin - as I did previously publicly declare my love for this anime on the Media Discussion board.  But my love for Saeko won't be denied...  

http://highschool-of-the-dead.wikia.com/wiki/Saeko_Busujim

For my orgy:
Fifth Harmony (5 girls singing group) - One is 17 (18 after June) so she can wait, but her four band mates can get Wackered (b/c they're all 18-21). KIDS OUTTA THE POOL! ADULT SWIM!;

For sheer flexibility:
Gabby Douglas - Olympic gymnast, age 19.  

and the Oscar goes to:  
Ashley Rickards - actress, age 2

but only b/c your subject "barely legal".  not really into young-ens.