Why does it say in the Jewish Talmud "A Gentile girl who is three years old can be violated."-Aboda Sarah 37a?

Gentile means anyone who isn't Jewish, for those who aren't familiar with that word. That quote, and many others which deserve to be read before forming an opinion about the Jewish race. I would like to know why they believe that a little girl can be raped if she is only 3 years old?