It's funny the ways that perspective can change; there was a time when the 6th grade seemed so grown up...some of it might have even been in 6th grade, highschool, college, on and on. I still say things like "when I grow up I want to..." sometimes it's in jest, a lot of times it's real. What is that makes you a grown up? Age would be one, but it's not always a gaurentee, I know men that are grandfathers that aren't grown ups.
I do sometimes feel like a grown up but not generally. I sometimes want to be a grown up, but sometimes I really don't. Sometimes I'd just like to go back to bed forever.