Coffee is not like wine which increases in desirability as it ages. The life span of good coffee actually last from about two days to about two weeks after it is roasted. The main reason for these dates is due to the gasses in the coffee. When coffee is roasted it stores up carbon dioxide within the bean which releases as it ages.
While this is some pretty cool science, why does it even matter?
Let's do an experiment with that last little bit of beans you have which was roasted two months ago. If we brew it up next to the fresh batch of beans roasted last week we will notice something staggering. The beans may be from the exact same bag of green beans and both roasted to perfection and yet they taste completely different. The two month old beans are flat and lacking flavor while the new beans are vibrant and exploding with great coffee flavor. There still may be some flavors in the two month old coffee but they are muted and a shell of what they once were.
So when you are looking to buy coffee from anyplace, be sure to check the roast date on the bag. It can make the difference between a good cup and a great cup of coffee.