Karen's age is stated as 15. Staci Keanan (Dana) is just over 5 months older than Angela Watson (Karen), and though it is hinted that Dana is the oldest, it was never made clear until this episode as Karen's age was never stated. In season 1 Dana is already 16 with her getting her license in episode 15 (Drive, He Said). This makes Karen and J.T. Both 15, even though Brandon Call (J.T.) is a year and five days younger than Angela.
First shot of the upstairs hallway. Outside of Frank and Carol's room and bathroom, only the girls room has ever been shown twice up to this point. It is unclear as to whether J.T. shares a room with his much younger brother and step-brother. All 3 girls share a bedroom as shown in episode 1.3 and stated in this episode.