Signs of Puberty in Islam

Islamically, one is considered pubescent/adolescent if one of the following things happen:

1. Pubic hair, which is the growth of coarse hair around the private part (Not according to the madhâhib ash-Shâfi`i and Abû Hanîfah)
2. Emission of maniyy from the private part
3. Menstruation [for a woman]
4. If none of the above happen, then when he/she turns 15 lunar years old

Maniyy for a man is semen, which is a thick, white liquid that gushes.

Maniyy for a woman is a thin and yellow fluid.

Imâm an-Nawawi said about maniyy: "The scholars said: When a man is healthy, his semen is white and thick, and gushes out in spurts accompanied by feelings of pleasure. After it has come out, it is followed immediately by a feeling of being drained and exhausted. Its smell is like that of palm tree pollen, which in turn resembles the smell of dough [...] Each one of these three characteristics is sufficient for it to be defined as semen; it is not necessary for all three features to be present. If none of them are present, the substance cannot be described as semen and in all likelihood it is not.
"All of the above applies to the maniyy of men; in the case of women, their maniyy is thin and yellow, although it could become white if the woman is strong. It has two distinguishing characteristics, either of which is sufficient to class the substance as maniyy: firstly, it smells like the maniy of men, and secondly, its emission is accompanied by feelings of pleasure and is immediately followed by exhaustion."

It is also worth noting that the one who is insane is not considered mukallaf.