Short answers, pulled from the story.
Adolescence is the transitional stage of human physical and psychological development between puberty and adulthood, usually associated with the teenage years. Scholars have not agreed on a precise definition, with some starting it as early as 10 and ending as late as 30. The World Health Organization designates adolescence as ages 10 to 19.
The average age of onset of puberty is 10 to 11 for girls and 11 to 12 for boys. Heredity primarily sets each person's timetable, though diet and exercise also exert influence. Puberty starts with a surge in hormone production triggered by the pituitary gland.
The brain reaches 90 percent of its adult size by age six, so it does not grow much during adolescence, but it rewires. White matter increases linearly while grey matter follows an inverted-U pattern through synaptic pruning. The prefrontal cortex, which governs decision making and impulse control, undergoes some of the most significant changes.
There is no empirical evidence for a significant drop in self-esteem over the course of adolescence. Barometric self-esteem fluctuates rapidly and can cause distress and anxiety, but baseline self-esteem remains highly stable across adolescence.
G. Stanley Hall founded the formal study of adolescent psychology with the publication of his book Adolescence in 1904. Hall was the first president of the American Psychological Association and defined adolescence as the period from ages 14 to 24, viewing it as a time of internal turmoil and upheaval.
Research favors the conclusion that adolescents and adults think about risk in similar ways but hold different values and reach different conclusions. Adolescents give more weight to rewards, particularly social rewards, than adults do. Most adolescent injuries are related to risky behavior such as alcohol use, reckless driving, and unprotected sex.