Do you mean the newer forums? If so you can should assume 9/4/04 is the day it went live. Judging from the Capts account. Older forums, I'm not sure. Though it wouldn't be to far-fetched to go with October 2002 shortly after AQ went live.
Wait, sorry I've only been around since 2009 so I'm not sure what you mean by the newer forums and older forums. Are you saying the original AE forums site was a different web address?