Lois says she is a Libra in "Contact," so her birthday is likely in September or early October. Her tombstone in "Tempus Anyone" says 1967, and Clark is February 1966.
Also, she says in "Lucky Leon" that when she was a senior in high school, she moved out after a huge fight with Sam. If her birthday is in the fall, she could have moved out sometime during her senior year because she would have been 18 and legally able to live on her own.
