It's 1987 and Jenna Rink (CHRISTA B. ALLEN) is a typical 13-year-old who can't wait to grow up. Although she's good friends with her next-door neighbor, Matt Flamhaff (SEAN MARQUETTE), she really wants to be part of the most popular school clique, the Six Chick Group. When they ditch her, she lashes out at Matt, and as wishing dust sprinkles down onto her, dreams of being a thirty-year-old.
The next day, Jenna (JENNIFER GARNER) discovers to her shock that her wish came true. Not only is she now in her 30-year-old body, but the year is 2004, and she's dating Alex Carlson (SAMUEL BALL), a New York Ranger. She's also an editor at Poise Magazine with the now grown-up former leader of the Six Chick Group, Lucy Wyman (JUDY GREER), with both working for boss Richard Kneeland (ANDY SERKIS).
Trying to take all of this in while faking that she's a poised, 30-year-old professional, Jenna has her assistant, Arlene (MARCIA DeBONIS), try to find Matt for an explanation of what's occurred.
She eventually does, but Matt (MARK RUFFALO) isn't exactly pleased to see Jenna. After questioning her odd behavior, he reminds her that they grew apart in school and went their own ways, with him becoming an engaged photographer and she a pushy woman that no one likes.
As she tries to process all of this new information, Jenna tries to save her floundering magazine all while finding herself falling for Matt and trying to act like a 30-year-old.