I just realized that I started my AD&D game exactly 22 weeks ago today. To date, we have missed but one session. We play on Wednesdays now, so tomorrow will be our 21st play session. The characters have only advanced about as far as 4th level (depending on the character), though I believe one is nearing 5th. Part of the problem is that they have amassed a large amount of treasure that they have been unable to get home or cash in yet. Still, I find that I am relatively unconcerned with levels, and the players seem to be less concerned than gaming groups are usually. The focus is definitely on exploration and interaction with the enviornment. We even had significantly fewer combats than your "typical" AD&D game (from my perspective, anyway.)
Honestly, I feel like we're just getting started... there are so many places this can go.