I just saw 500 days of Summer and was thinking if maybe Rachel Hansen, acted by Chloë Grace Moretz at 12 years old, is maybe in reality much older.
I mean, we all see what happens from Tom's point of view. The scene in the park with everybody dancing around him is clearly only happening in his imagination. So my theory is that Rachel is maybe around 20 years, but since she is Tom's younger sister he sees her as a little kid (and her teammates too).
She is clearly more mature than that, she talks about past boyfriends and she goes to Tom's house at 10:00pm because Tom's friends call her. They trust in her being mature enough to handle Tom. Nobody else treats her like a child, except Tom.
I think Rachel is much older but we see her as a 12 yo because we see her trough Tom's eyes and in his imagination she is still his little sister.