Indeed, Minecraftonline out-dates 2b2t by a number of months. It's a minute amount, but still important. With that said, 2b2t is the oldest Anarchy server still around. A common youtube video publicized it without select information, such as the whole "anarchy" part (Meaning that 2b2t was thought to be the oldest to many viewers, although it was just poor phrasing, word choice, and very select information that caused the youtuber to portray false information to a vast sum of viewers.)
Apologies for bumping an old post, There's still a server around called Novylen (Ip: mc.novylen.net) The server still runs a pre-mp map and I believe went up day one of multiplayer becoming available, hasn't been down since. The community is still amazing to be a part of and some of the builds that exist from the alpha days are simply breathtaking.
Apologies for bumping this post once again, but in answer to Dograffe's comment, I have to add that MinecraftOnline went up within *hours* of the announcement of SMP. This would make it older and far more populated than Novylen (MCO always has at least 3 or 2 persons, up to 15 sometimes in a good time, although the server has space for 12000 (not a typo) while Novylen was empty when I visited it (today), had a 20 player limit, and the blog hadn't been updated since 2013.)
I run mc.novylen.net and if it's not among the very oldest servers, we're certainly within a couple hours of it. The server map went up the same day of SMP announcement and the release of the Java binaries. I used my old infdev map to start things up, too. Good times. I still have the shell script wrapper I used to hack some management commands in, somewhere.
Yeah, it's a small server, nothing big or impressive like minecraftonline, and over the years, I've reverted back to a really straightforward survival map. We've had minigames maps, creative worlds, skyblock, etc, but after a while, I only have so many f***s to give, so I keep it at a small and tight user community. Anything more than that and I burn out.
Guilty as charged on the blog post thing though. I should probably do an "I'm still alive! I don't want to get on the cart!"