Because she appears childlike in the film, I was curious how old Dottie Smith is in Killer Joe?
I don't believe it is ever explicitly said in the film, but it is supposed to be 20. This is what is stated in the play (see here for a link to a "snippet" from the play).
A lot of the confusion/controversy in the film comes from the "chicken" scene, where she mentions she is 12. This has been discussed by several people involved in the film, including Matthew McConaughey:
"The way I understand it," said McConaughey, "the MPAA's NC-17 rating is really about the chicken scene."
SPOILER ALERT: Skip the next paragraph if you don't want plot revelations.
Indeed, whatever mark "Killer Joe" may leave on America's movie conscience, it will forever be remembered for the "chicken scene," in which Joe forces Sharla, in front of her husband, to perform mock oral sex using a chicken leg. It is a seriously messed-up moment that spurs more violence.
Initially, McConaughey thought the harsh rating was because of a sexual scene between Joe and Dottie, in which Dottie recalls a physical encounter from her childhood when she was only 12. If you don't quite catch the dialogue, you might think Dottie, who is supposed to be 18 or 19 in the film and is played by the 23-year-old Temple, is saying she is 12.
"I thought that's what the MPAA was having trouble with, and I thought that could be a simple fix, raise the volume a bit, or get a line in there, 'How old were you?' The reason I thought the chicken scene was in the realm of R is because it's so deliberately provocative. It's hyper-reality. It's got so much what-the-F to it. It's the classic comedy setup. I thought there was something about the deliberation of it that lets it be absurd and lets you laugh, in the way that Tarantino can get away with some of that stuff."
The producers and Friedkin appealed to the MPAA.
"I believe it came back to, 'There are 20 or seconds that need to be cut.' And Billy was very clear, 'No way.' And I was on board with him. 'Please, no. That's it. Let's wear NC-17 as a badge, and shine that badge and go forward.' "
However, it appears this confusion is something that has affected many online, with plenty of commentators incorrectly referring to her as being 12.