I've always assumed beans are fresh for about 2 weeks from roast. So you have about 3 days for them to outgas, then after day 14 or so, flavor starts to fall off.
The other day I visited a local Brooklyn roaster, and saw the beans for sale were all 10 days old or older. So I asked the barista/sales-guy if there was anything fresher, and he said, "Why?" I said, well, 14 day window, etc etc. He looked at me as if I were from Mars and said, "Beans are good for 2-3 months, depending on the lightness or darkness of the roast." He was a bit supercilious about it, but whatever. Anyway, I'd love to be wrong here, as I end up worrying if I'm going to go through a batch before they start to fade. Of course I'm not saying on day 15 flavor falls off a cliff, but anyway I'd love to get people's insights on this.