Neither of my nieces have ever been on a cruise before. And since I'm not their parent, I feel a little extra-protective. (their parents left it up to me; I wouldn't think of letting her check herself in and out if mom and dad were not ok with it)
My elder niece is 13 and will be in the Edge too. I'm comfortable with the fact that she will be able to sign herself in and out. Plus, I can give her one of the Wave phones so that way I can always call her if I am wondering where she is. That's my biggest problem with letting the younger one check herself in and out- unless I pay extra to rent another wave phone (and risk her losing it), I won't have any way to find her if I don't know where she is.
When I was originally telling them about the cruise, my older niece kinda wanted to go to the kids' club instead of the tween club.

She is a bit young for her age socially- although very mature otherwise.
I've been having lots of hard stuff going on at home so I keep thinking about Disney in order to keep myself (semi) sane.