I wasn't clear.... The new registration appeared to happen prior to turning off the age check. As I follow the sequence of events, the first user hung due to the Twitter required setting. Not knowing about that, I tried to manually create his account. At that point I received the duplicate email error.
After turning off the Twitter required, I was able to create an account for one user. But, the one user I received the dup email still would not work. I was able to contact that user and he tried to register with a different email address. That worked fine.
As you noted a possible error linked to the age requirement, I shut it off. Then I noted the Users Awaiting Approval had been incremented. I was able to see a new user request. So, three new users were logged. I am not sure if the age requirement off fixed anything. I do know the Twitter switch appears to be problematic.