I remember when I was a kid I thought everyone over a certain age was equally "grown up."

I didn't have a really clear idea of what that meant as a kid, of course. But it was like, after you reach a certain age you are grown up and that's it. There is no more learning or development. So in my hazy mind's eye as a child, a 23 year old was an adult, same as a 33 year old, a 45 year old, or a 60 year old. They were all the same to me. Then you have the category of "really old people with gray hair like grandparents."

I think a lot of kids think this way. Now, of course, its hilarious to imagine a 23 year old and a 55 year old being equally wise and mature.