DoG was formed in 2004
ESO wasn't out in 2004.
and our guildmaster started this guild in ESO's NA Xbox 1 megaserver on day one, so Yup!
Other guilds were created on Xbox on day one as well, some that were already in existence in ESO on PC. They might even have used characters imported from PC, so they would have been able to create the guild before your guildmaster reached level 10. My guild, for example.
I might be splitting hairs, but isn't it a bit presumptuous to claim to be the number one oldest ESO guild? Even with my guild, that was created right at the beginning of the PC beta (it was in the works but not officially created during the alpha), transferred to the full game on PC a day before day 1, and transferred to xbox immediately after logging in with imported PC characters in the first hour of the game's console release, I only claim it to be one of the oldest guilds in Tamriel, not the oldest. And as far as old guilds outside of ESO that now exist in the ESO space? I know of at least two that were started before 2004 just offhand.
I'm not trying to start something, it just seems a bit rude and arrogant to claim to be the best at something when it isn't the case.