Psychologically I should say that a person becomes an adult at the point when he produces more than he consumes or earns more than he spends. This may be a the age of eighteen, twenty-five, or thirty-five. Some people remain unproductive and dependent children forever and therefore intellectually and emotionally immature.
In the last analysis, the individual person is responsible for living his own life and for finding himself. If he persists in shifting his responsibility to somebody else, he fails to find out the meaning of his own existence.
To be a man is to be responsible. It is to feel shame at the sight of what seems to be unmerited misery. It is to take pride in a victory won by one's comrades. It is to feel, when setting one's stone, that one is contributing to the building of the world.
I am responsible for everything except for my very responsibility, for I am not the foundation of my being. Therefore everything takes place as if I were compelled to be responsible. I am abandoned in the world... in the sense that I find myself suddenly alone and without help, engaged in a world for which I bear the whole responsibility without being able, whatever I do, to tear myself away from this responsibility for an instant.