Short answers, pulled from the story.
Adolescence begins with a chemical explosion triggered by a surge in hormone production from the pituitary gland. This biological revolution activates the gonads to produce testosterone in boys and estrogen in girls. The timing varies with girls typically starting between ages 10 and 11 and boys following between 11 and 12.
The adolescent brain undergoes synaptic pruning and myelination to increase efficiency rather than size. The prefrontal cortex responsible for decision-making does not fully mature until the mid-twenties or early thirties. White matter continues to increase until around age 45 while grey matter follows an inverted-U pattern.
Adolescence is defined by a search for self that manifests as a turbulent identity crisis. Teenagers develop metacognition leading to the imaginary audience and personal fable. This cognitive shift allows them to question authority and move from concrete to relativistic thinking.
The social focus shifts from family to peer groups who become the new reference for identity formation. Cliques and crowds form to provide belonging while introducing risks like peer pressure. The home environment remains a crucial safety net despite conflicts over control and privacy.
The average age of first sexual intercourse in the United States is around 17 years old. By age 15 more than half of adolescents have experienced a romantic relationship lasting at least one month. This period brings a mix of heightened romantic interest and increased vulnerability to risk.
The formal study of adolescent psychology began in 1904 with G. Stanley Hall. He viewed the period from ages 14 to 24 as a time of storm and stress. The World Health Organization now designates adolescence as the phase from ages 10 to 19.