I guess it kind of depends on how we're going to measure "maturity", but whether girls mature faster or not I think it's fairly undeniable that a lot of the time males are more stable than females. Sure maybe guys will be making fart jokes and lame sexual comments well into their teens, but on a gender basis it's generally not the guys that go off the wall for no apparent reason when "that time of the month" comes around. Even without the hormonal imbalances that the menstral cycle offers, in my experience it's usually woman that have the volatile personalities more so than men. Not that that answeres your question...
As I said before, it's dificult to exactly "measure" something like maturity. I think a lot of the problem is that people (younger ones especially) use imaturity as a form a amunition for arguments. The "well that's immature of you, my side of the debate is more grown up" scenario for example. Personally I think it boils down to the person, not so much the gender. Though it's be said that females have a high rate of maturity per capita than males, so I guess we'll see about that.
I think it's largly situational as well. Odds are a girl mid-cycle being all unstable and whatnot is going to seem a hell of a lot less mature than the average Joe type of guy when she goes off screaming and crying and yelling about apparently nothing, but just the same when a guy's doing some sort of macho presentation as we are apt to do at times and the girl's just having a normal day the inverse would likely seem apparent.
What sixstring said. Girls in their teens are more mature, but overall men will overtake women in maturity levels. I read this the other day in my textbook, but now I can't remember. But yea, guys overall become more mature, but I'm not sure who matures faster. I'm not even sure if it should be gender based, maybe personality/intelligence based.
I think besides it being (mostly) individual, it also depends on the situation or context.
So let me use one with shock value: picking up girls as a teen guy/being a teen girl. My opinion: a large amount of girls are absolutely STUPID things when it comes to this. I don't know if you paid attention to this in high school or not, but the guys with a lot of girls were quiet geniuses in that field. They learned how to be master manipulators and land the girls. This stuff doesn't matter to me so it's not like I look up to them. But when people say that girls mature faster, that makes me think they are more mentally capable and intelligent things but they aren't. All it takes is some relatively simple emotional appeal and/or manipulation, then they are falling all over a guy. Those guys seem primal but they're smart enough to let girls think that guys are stupid.
But in more important aspects, I think it's pretty down the middle. The girls and guys I went to school with didn't seem any more or less mature than the opposite gender.
depends on the individual. I'm 20 and am more mature than many girls my age and less mature than others, but generally speaking I think that people of similar age have been exposed to similar environments are around the same maturity wise.
Its a toss up between both in my opinion, some can argue that guys do, and others can argue that girls do. I think its in the middle, each gender has some immature ones that weigh down the mature and make people judge them based on that.