The thing is, we get that scenario that you gave with the hangouts and circles with Facebook, which teenagers use all the time. And, again, those questions you brought up are part of the legal gray area I mentioned above, of how much control the government and parents should have over how teenagers can use the internet.
I think the main frustration I have here is that I have other friends who never gave their ages to Google - i.e., who never signed up for a Youtube account - who have been able to get onto Google Plus. (I know because they keep sending me invites. It's quite aggravating.) Which just goes to show that Google's rules aren't even being evenly applied across the board.
But hey, fair enough. As I said at the end, I just hope they get out of the field trial stage soon. And for now, I'm off to make a new anonymous Google account. :)