Really interesting topic! Actually loving reading the responses, I really enjoy seeing how everyone matures, and what they think constitutes an adult (not to say that any particular person is right or wrong here - being something is all about what you attune it to, after all)
So, from the age of 15, I've changed a lot - there's the bits about my whole interests and career path changing drastically, which I've talked about before. Also when I was about 15 I was incredibly depressed and suicidal, so there's the obvious change in which I've recovered a lot from that.
I think the biggest change I've gone through is really accepting myself and who I am, particularly in terms of sexuality. It might seem weird to pick such a specific one to be sexuality, but definitely when I was younger I was very much the typical boy (which is funny since I was also a bit of a nerd, socially awkward, and picked on by most of my peers), who did the whole "o yeh lololol penis in her vagina the ho be mine", but secretly thinking it was disgusting and not wanting any part of it. Then I went through the whole "wow, you had sex with him/her?? Ummmm I don't see a wedding ring?

? Slut." stage, and simply refusing to talk to anyone about anything of a sexual nature, immediately getting awkward and making an excuse to get away from them.
Whereas now, I'm much more open about it - I'm more than happy to have discussions of a sexual nature with people. I'm happy to talk about how to keep it safe, how to keep it pleasurable, listen to people's adventures in the world of hook-ups, and am definitely not judgemental about it at all. Which kinda sucks, because I see the judgemental parts in a lot of first years, which I find disappointing given the amount of people who live sexually-charged lives. Like, it's completely natural - it's how most of are around today. There's no need to shame people about enjoying it. Not to mention, the constantly using gay as an insult, thinking homosexuality was bad, and now being comfortable in the fact that I am, actually, queer.
Another way that I've grown is my acceptance the fact that I have Asperger's syndrome. This used to really upset me, since I could never tell what people were thinking, always felt excluded, would get massively anxious in social situations because I had no idea what was going on at all. But, now I can own it, and despite still struggling in identifying social cues, etc., I no longer beat myself over the fact that I just won't be able to pick all of them up.