I think that girls mature faster than guyys because girls normally start puberty earlier than guys. Girls start puberty as early as 9 and stop at 16 or 17, while boys start puberty at least at 11 and stop at 18 or 19. However, some boys go through puberties that prolong to age 21. These differences also explain why most girls around 18 tend to act a little more serious then most boys at that age.
that is true but i've seen some guys who are way more mature (including me) than girls but you are right but sometimes its not always 100% correct
Don't get mixed up between physical and mental maturity. While girls certainly mature faster physically, that doesn't mean mentally as well. Mental maturity is comprised of adult, elitist labels which can't be credited. By that I mean to say that there isn't a way to measure the mental maturity of a person as any such diagnosis would be purely opinionated.