Research suggests that by ___ years of age boys behave more independently and less compliantly than girls.

By the age of 2, this begins to take place. Boys are given the latitude to "explore" and "be boys," while it would be considered "bad" for a girl to do these things, especially at so young an age. Girls are socialized to be compliant and demure, instead of being given the ability to explore their surroundings and try to learn about the world.