I define angst as a feeling of frustration over undesirable and nebulous circumstance. It is anger, anguish and turmoil felt when the vagaries of existence cause one to feel powerless. When a situation cannot be confronted or solved, and the implications of being a part of it have far reaching consequences past the immediate time and setting.
I don't associate it with teenagers and immaturity. I feel that age range gets this appellation due to the particularities of neurochemical changes that occur around that time in our lives. Eventually, because of the literal immaturity of adolescence, it causes a negative, condescending connotation when used.
But I generally associate it with the outcast and the passively ostracized.