At the beginning of the movie, on the phone, Michael tells Julianne that Kimmy is 20 years old. Then a day or so later, in the karaoke bar, Kimmy is served a beer, no questions asked. Is the drinking age in Chicago 18?
You know what? I know it's scandalous, but I've actually heard of UNDER-AGE people getting served in bars. Horrific, I know. That would be especially true since she was there with two 28 year-olds.