My current oldest is from early 1999. My club planned ahead for a "Millennium Party", for the turn into the 2000's. Members were asked to brew a beer of at least 100 gravity. (Note: this was an overnight party. Bring a sleeping bag, turn in your keys.) I brewed a Belgian "Quintuple", or a "Double Tripel", which fairly accurately describes what I was going for. OG was about 1.130, FG about 1.030. It's bottled in champagne bottles, originally to about 7 volumes CO2, but the last one I opened (last month) was mostly flat. The biggest surprise to me is how much the color has darkened. It was golden, it's now a medium-dark amber. It's picked up a strong sherry note, but unfortunately has an unpleasant oxidation note also. I've still got a few bottles left, which come out for homebrew gatherings.