I'm 26, male.
This is a tough question because there is no gauge to really measure maturity.
However, just speaking loosely, I think I'm very mature in some ways but extremely immature in others. Over-all, compared to a lot of people I know, I guess I'd consider myself fairly more mature than average. Although certain aspects of my personality would make me appear, on the surface, to be very immature compared to others.
Ways in which I am mature: I am responsible, trustworthy, and considerate in the general sense. I have a very calm demeanor. I have very good reasoning abilities and am capable of seeing multiple viewpoints for every issue. I always get along great and have great conversations with people in their 40's, 50's and 60's- sometimes more so than with people my own age. I have a strong tendency to think about and appreciate and relate things to the big picture of history. I feel way too mature for teenage-oriented musical styles and related trends (like emo and goth, for example) whereas I frequently see people in their late 20's and even in their 30's that are still totally immersed in all that sort of thing and they seem like they still relate to juvenile emo singing. I almost always think about the long-term affects of possible actions.
Ways in which I am immature: I feel very immature inside, like I am still a kid, just in general. I still like to play and imagine things like I did when I was a kid. I don't know or understand a lot of important little things that adults typically know all about, like stuff about insurance and mortgages and stuff like that. I get excited when I pass the toy isle in stores. I guess in general, I look very young in my physical appearance (at 26, I probably look like I'm about 20) so that makes me automatically feel like other people probably view me as immature, which makes me sort of feel immature.
That's all I can think of. I just spent a long time really thinking about my answer to your question. I hope you appreciate it.