Previews make it look a lot like Big, but it is possible to identify some differences between 13 Going on 30 (rated PG-13 for some sexual content and brief drug references), the first starring vehicle for Alias's Jennifer Garner, and the 1988 Tom Hanks film. For one thing, in Big the protagonist was 12. Here, obviously, Ms. Garner's character starts out as a 13-year-old.
More significant to the plot, though, is that the magical transition from child to adult takes place in real time in 13 Going on 30. In other words, rather than a child waking up in an adult's body while everyone else around him stays the same, as in Big, 13 Going on 30's Jenna Rink flashes forward from 1987 to 2004 to inhabit the body of her 30-year-old self.
Jenna is an awkward girl who wants desperately to fit in. Despite the encouragement from her best pal Matt to be true to herself, Jenna has just one desire: "I don't want to be an original. I want to be cool," she cries. Jenna is ahead of her time, though. More than wanting to fit in with the cool girls at school (called The Six Chicks-the cool girls always have a name in movies like this), Jenna wants to be the kind of beautiful, successful woman featured in her favorite magazine, a glossy fashion monthly called Poise.
A particularly awful 13th birthday party, combined with some plot-convenient "wishing dust," transports the distraught Jenna to her dream life. She's not only 30 and beautiful, she's an editor at Poise. She has everything she could ever want, right? Of course not. Her adult life, seen through the eyes of a 13-year-old, quickly loses its glamor, and she learns some Important Life Lessons on the road back to her teen body.
Notwithstanding significant advancement in the age-switching plot device (of which Big is just one prominent example), it will probably surprise no one that 13 Going on 30 is not in the least bit surprising. The film succeeds in being mildly amusing, but it's not terribly appropriate for the preteen audience most likely to appreciate its mild humor and simplistic (though worthy) lessons about being nice to others and true to oneself. Although relatively subdued by PG-13 standards, there's quite a bit of sexual innuendo in the humor.