Most of the voice change begins around puberty. Adult pitch is reached 2–3 years after the onset of puberty, but the voice does not stabilize and does not reach its final tonality and pitch until the early years of adulthood. It usually happens months or years before the development of significant facial hair. Under the influence of androgens (a bunch of hormones, including Dehydroepiandrosterone (DHEA) and androstenedione), the voice box, or larynx, grows in both males and females, but this growth is significantly more prominent in boys. The result is: the voice drops and deepens. In parallel with the changes in the larynx, the vocal cords grow significantly longer and thicker.
The facial bones also play a role in the voice maturation: cavities in the sinuses, the nose, and the back of the throat grow bigger, thus creating more space within the head to allow the voice to resonate. Occasionally, voice change is accompanied by unsteadiness of vocalization in the early stages of untrained voices. Due to the significant drop in pitch to the vocal range, people may unintentionally speak in head voice or even strain their voices using pitches which were previously chest voice, the lowest part of the modal voice register.
Genetics also play a role in how our voices mature. Although how a child’s voice develops owes something to mimicry of their parents, people from the same family will often sound alike because laryngeal anatomy is dictated by your ancestral DNA just like every other physical trait. It’s the slight variations around this anatomy that make our voices distinct.