It seems many people in your comments don't understand what leadership is. Leadership does not involve bossing people around, or in fact even having people "below" you.. Leadership is a way of living that teaches by example.
Those who live that way do tend to be put in leadership positions eventually - but it's not required to act as a leader.
I get your meaning completely. You're saying a boy becomes a man when he is self aware enough to govern himself in a way that others follow.
For example, my son in law is 28, but he is still a boy. And it's because, even though he's a father of 2, he does not take initiative. He spends more time playing with his kids and riling them up than teaching and guiding them. My daughter has to say, "Let's clean up" "It's time for bed" "Let's use our inside voices" to him and the children. He should be taking the initiative. He, too, knows what needs to be done (or at least he should).
For someone without children - like my sons who are 19 and 21 and still live at home, it could look like them seeing we're out of milk and taking initiative to pick it up themselves. At work, instead of waiting to be told what to do, they could choose to take the initiative and do the tasks they can see need to be done.
Just because you are acting as a leader does not mean you have employees or family members under you. ANYONE can take up leadership responsibilities without being given a title.
Great article. Not sure why all the push back.