Average album age: 8.6 years (that average is greatly skewed by Neil Young).
Interestingly enough, Harvest is also the only album in this list that was released by a major record label. In fact, it's the only one that I physically own; I purchased all of the others online. Quite frankly, a very small percentage of music I like was made in the past 5 years and was produced by a major record label.
I blame the Shmoos.