Puberty is the time during the growth of a person at which sexual development occurs, commonly associated with a growth spurt. Female puberty involves several stages – the acquisition of breast buds (see mammary glands); of sexual hair, and the onset of menstruation – which may each begin at different times. Male puberty involves sexual-hair development; voice change, and growth of the testes and penis. Precocious puberty is when the pubertal features develop abnormally early (before 9 years in females). The average age of puberty has fallen in recent years.