Possible Clues:

• Typical middle schooler, agewise
• Many a millennial during the 1990s
• 11-year-old, for one
• "Not a girl, not yet a woman," to quote Britney Spears
• Sixth-grader, typically
• One at an awkward age
• In the midst of, poetically
• Shopper in the juniors section, maybe
• Many a Disney Channel viewer
• One that's not quite a teenager