Yeah, it swings both ways.
I was 22 when I moved out (and my parents wanted me to stay). I think I was ready then. I had money saved.
It's a mix. There are lots of responsibilities to living on your own. You really have to depend more on yourself for things (it's the little things like when your toilet doesn't stop running the first time, and it's overflowing, and you alone have to handle it (before you call maintenence), that are the scary and gradifying moments of living on your own.
On the flip side, unless your parents have no interest in you, there are obligations to tell them where your going, etc. It got old after awhile, it's great now that I just go where I want (if the wife let's me), and no parents lording over me. It really makes you feel like an adult.
So, there is no right or wrong time to move out. It's really a personal thing. For some, it's 18 and out. For others, hanging around is the right move.