Boys grow their fingernails long because because they're too lazy to cut them. Girls are attracted to boys, even at an early age. At an early age, boys are attracted to dirt. By the age of 6, boys will stop giving their dad kisses. By the age of 6, girls will stop giving their dad kisses unless he bribes them with candy.
Most baby girls talk before boys do.
Before boys talk, they learn how to make machine-gun noises. Girls will cry if someone dies in a movie. Girls turn into women. Boys turn into bigger boys.