I don't remember exactly, but it was a few months ago. About a month ago we also launched the ability to create "child" accounts for under-13 users who aren't old enough for Google or Facebook accounts.
Sorry, it's not possible, but the main reason to create a child account is to get around the Google/Facebook requirement -- since you've already surmounted that hurdle, a child account probably wouldn't be of any more use to you.
