You're getting old, dear. Did you know? "Saturday Night Fever" is 48 years-old this year, or like many of you, within spitting distance of 50. "How can this be?" you ask in horror. Sorry, Margaret, get out those crutch tips. Time marches on for everyone. Fun facts: The movie was based on a 1976 New York magazine article -  "Tribal Rites of the New Saturday Night," by British author Nik Cohn  - which was a complete lie. As in totally made up. No, really. He was a newcomer to the U.S., didn't know the Brooklyn disco scene at all, so he based "Tony," the lead character, on an English, so-called "mod fellow" he knew. He also pocketed a nice chunk of change from Paramount and producers when they bought the rights to the article, thinking it was real. Smooth move, Nik!  As for the casting of Donna Pescow, this was based almost entirely on her looks. Studio executives Michael Eisner and Jeffrey Katzenberg initially thought she was ...