People think of different things when they say the word "maturity."
Certainly "age" doesn't necessarily make anyone more intelligent, responsible, considerate etc etc
But there is something to the reality of just having lived longer. There are just certain things you cannot learn, you just have to live through them. There are certain perspectives that young people will just not share with those older than them (general statement).
I was always a responsible person. People have always told me I am mature for my age, even in my teens. But I am not the same person I was 5,10,15 years ago. Just living changes people.
I'd have a tough time dating a girl older than me. I'm 27, and lets face it -- most single women around my age are looking to get hitched ASAP. That's not for me, so I usually find myself attracted to the 22-24 age bracket.
I have dated guys as much as 11 years older then me no biggie in my book as long as you didn't pick her up at loose change loise those girls are trouble.