It's mostly in detail. You should draw the chest part more wider and don't draw the hip so small, since hips are what give emphasis to females. Add details of the jaw, emphasize the angled line to make it more masculine as compared to that of a female character. In drawing the shoulders, emphasize on the angles imitating the trapezius muscles and the collar bone. Hope this helps out!! :D This is what I use when drawing males.
