Should a girl know what a penis looks like by the time she is 13 years old?

At thirteen, most girls would at least have an idea of what a naked man looks like. She probably shouldn't necessarily have actually seen one, and certainly shouldn't have examined one closely. There are several websites where you can find anatomical photographs that are not porn sites. In fact, just type 'human penis' in the question box on this page and you will be directed to the Answers.com page with illustrations.