In episdoe #82, Class Reunion, Andy and Barney are said to be graduates of the class of 1945. In episode #176, The Return of Barney Fife, there is a banner at the class reunion that reads Class of 1948. In addition, both Andy and Barney mentioned having served in WWII (Andy in episode #6 Ellie Comes To Town, Barney in episode #29 Quiet Sam) which would have been impossible since the war ended in 1945.