- Boys can begin puberty as early as age nine or younger. Initial indicators include the beginning of body hair, increased skin oil and deepening of the voice.
- At approximately 11 years old and as testosterone increases, the scrotum will deepen in color, the penis grow in length and circumference and the testicles will increase in size. This development can last until age 14 or later.
- At approximately 12 years, the boy's muscles will increase in mass while the bones will lengthen and increase in strength. This skeletal development can last until age 18.
- As a result of increased testosterone, the boy's vocal chords will grow thicker and longer, so the voice deepens. This begins normally about age 13 and can continue until age 15.
- As hormonal levels increase, spontaneous erections will be more common, starting as early as 9. Due to increase semen and sperm production, the boy will have increased nocturnal emissions, or wet dreams, starting at about this age and continuing until becoming sexually active.
- Boys also begin to appreciate and engage in more abstract thinking as the brain develops. Influenced by family life and school, boys can become more interested in politics, religion, philosophy and goal-setting from age 11 until adulthood.
