Not sure the exact date, but it was right around the same as rabid I believe (1.5 years). I would also say that due to so many of the oldest players leaving, right now 1.5 years could be considered old. There really isn't that many active players who have been on over 2 years. What like 15-20 maybe?
His "extra month" doesn't count because the server was not public and not "ecocitycraft", merely something run for private enjoyment. I am still the oldest user.
According to this thread I am One of the 25 oldest active players! I am so faaaabuulooouuussss! Another thing you had to be a lucky player to find ecc in 2011, it was very hard to find. I went through 46 pages after searching for "economy" on minecraftservers.net. Well it was worth it!
Might I propose a suggestion? I would post our join dates (or a rough average within a couple days of assumed join date), so that it won't require editing the post every week/month.