OK - I have figured out the mystery of how my co-workers misjudged my birth year.
One of the women in the department knew that she and I had both graduated from high school in 1978. Figuring that if I was six when I started the first grade, with a birthday in November, they deduced that I must have been born in 1959.
Math was fine - but they didn't have all the facts. They didn't know that I was the last kid at home and Mom was ready to have all her kids in school. So, since I could already read and count and was unusually tall for my age when classes started in September of 1966, she took me to school registration and talked the school into letting me start at 5. Thus started my school career of always being the youngest and the tallest in my class. (And in a roundabout way set me on the path for criminal activity in the great pumpkin heist of 1978 when I was a 17 year old college freshman - but that's a story for another day.)