In girls puberty begins from 12 and lasts at the age of 18 . Girls gain maturity earlier than boys due to this only. Girls get mature because of the many reason
Gender biased society
It is believed that being a girl is a sense of responsibility . If you are a girl than you have to be polite and responsible . So it is like normal things .
Maturity rate
In india , the girls are allowed to get marry at 18 only but boys are allowed to get marry at the age of 21 . This is also the reason why girls grow elder .
Responsibility
Girls get more responsibility than boys. At home also girls are supposed to take care of their home . Organise the room, clothes. This is what fed up in our mind since we born .
Onset of menstruation
This is also one the reason . During this , several hormonal changes are there and development of body . So they prepare a tendancy of being adult .
That's why girl child gain maturity earlier than boys. Hope you are satisfied with my answer.
Thank you!!