so it seems that McTrAyN and amp27 are the two youngest that have come forward so far.
previous youngest member that I can recall was Steven11 (who was 11), when he became 12 he changed his profile name to steven12.
then changed is again to something else, (webmonkey I think).
he was also the youngest mod also I think, though his modding abilities were restricted to just a couple of forums.