Here are some great words from Scott McKnight's blog regarding a definition of manhood. I find these words incredibly refreshing, simple and sensible in contrast to so much of the oppressive and rigid gender stereotyping that seems to be constantly heard in so much of the evangelical community today.
"I think “manhood” is for an individual male — with whatever talents and gifts and context God has granted to that person — to follow Christ in such a way that brings glory to God in relationship to God, self, others (spouses and children included), and the world. When the male follows Christ, we see what genuine “manhood” really is. To follow Christ, to put it in Jesus’ own terms, is to love God and to love others (as the self)."