I suppose there are multiple ways of answering this question. Ultimately it comes down to how an individual defines what being a (man) or a (woman) is to them.
One answer might be with time all boys and girls physically become men and women.
However there are many people who go beyond physiology and instead determine whether or not a man is a "man" or a woman is a "woman" by how they conduct their lives.
"A (real man) would ...etc" or "A (real woman) does...etc" which has nothing to do with physiology and everything to do with (their expectations and beliefs).
Some would say a 30 year old unemployed male who lives in his parents basement and plays video games all day with no ambition is not a "real man".
However if he committed a crime he wouldn't be sent to a juvenile facility. On the other hand it makes no difference how mature a 14 year old is they're still a child. Age is a factor.
I believe being independent and taking responsibility for one's own welfare is adulthood. Essentially if that (adult) is a male or female will determine if they're a man or a woman.
Having said that some people don't want to "grow up" and enjoy being dependent. In some instances if a person isn't getting what (they) want from a mate they'll accuse them of not being a man or woman because he/she isn't doing what (they) want.
What makes a man become a man?
Ambition and desire to be in charge of their life.
One man's opinion!:)