The PVK Proportions game #1 just past the 3 year aniversary a few days ago, it started on March 29, 2002. At turn 261 that's about 1.6 turns a week on average. I was in the game at the start but dropped out over two year ago.
We have one game still running that's older. The Borg Open challange game, started in July 2001. That one is only up to turn 167 so they don't do turns as often apparently. It's probably about to wrap up since there are only two players left.
We have three games with more turns then the Proportions game. Currently the leader in that department is TDM Round 2. This game is on turn 361. It's only a two player game, which tend to go faster. They started in June of 2004 so they have done better than a turn a day for almost a year now.
We don't keep stats on games that are finished and have been deleted so I can't tell you what the most turns in a game ever is, but I'm pretty sure the oldest game ever is the BOC game. It's almost as old as PBW.
Geoschmo