The movie 13 Going on 30 seemed like it was going to be, and was, something like the 1998 Tom Hanks movie Big only with a girl protagonist.
I liked the fantasy element and the message, which is about being loyal and genuine and appreciating the now. Overall I thought it was cute and fun to watch if rather awkward in places.
The idea of magically becoming a different age is similar to the idea of body-swapping in movies like Freaky Friday (1976 and 2003), whose premise is that a girl changes bodies with her mother, thus gaining an adult perspective.
One review I read pointed out a similarity with Devil Wears Prada (2006): there’s a backstabbing New York career plot element.