It really depends on the roaster and the beans!
Some beans might have had it by 14 days....some only just begin to peak then! The coffees I use at work, I try not to use until day 10 onwards....I find most of our blends peak between day 14/15 to early 20s. One blend in particular will last longer and is still bubbling away like crazy after 17 days like it just came out of the roaster!
General rule of thumb...the longer the roast time is for the blend/coffee, the more CO2 youre going to produce. This means you need a longer resting time before you should use them...otherwise they will take on an almost green flavour because its too fresh.