Puberty is the time that an animal first acquires the capability of producing viable gametes. The puberal transition is rather unobtrusive in males. Commencement of estrous or menstrual (ie., menarche) cyclicity is a perceivable landmark. In some females (eg., rodents) the vagina is imperforate before puberty (estradiol of follicular origin stimulates vaginal opening).
Body condition is more important than chronological age (Table 5-17) in predicting the time of puberty. There is debate concerning the nature of the metabolic cues that trigger puberty. Some researchers claim that puberal incipience is a function of percentage body fat. Indeed, recent studies indicate that leptin, a hormone released from adipose cells, interacts with a kisspeptin, a product of the hypothalamus, to mediate the onset of puberty (and perhaps other metabolic states that link fat mass to reproduction). Others argue that puberty is more closely related to rate of growth per se (ie., the prepubertal growth spurt). Regardless, any disturbance that intercedes normal progress of somatic development (eg., GH deficiency, hypothyroidism, Addison's disease/adrenalectomy) will delay puberty. There is inferential data that melatonin is involved in the timing of puberty in humans. As a general rule, mammals reach puberty at or about two-thirds of their mature body weight. Females are a bit more precocious than males. Ages of puberty of European and North American children have decreased significantly during this century; this is undoubtedly related to improved standards of living (ie., nutrition).
Puberty can be distinguished from sexual maturity; these processes are separated by a period of adolescence. Puberty is a physiological state. Sexual maturity commands additional physical, psychological, and social integrals. The male is judged sexually-mature when he has achieved the stature needed to successfully impregnate a female. A female is considered sexually-mature when she can carry a fetus to term and provide adequate postnatal care for her offspring. From a responsibility standpoint, some of us, in the strictest sense, never become sexually-mature.