The time it takes to become proficient varies upon the style and your own abilities. In most self defense systems, you should feel that you could defend yourself fairly well after six months. To reach black belt, the same variables are in play, but somewhere between three and five years is about right.
Most instructors recommend two classes per week, plus time in between classes.
You should match your involvement with your fitness level. At this school, the students are grouped by age and rank. This means that you should be in a class with other beginners and lower ranks. At this school children learn that the martial arts is not an act of violence, but the art of how to handle themselves in a problematic situation. Aggression should be channelled into assertiveness to increase a child's self esteem and build discipline and character.