When coffee is roasted, gases form within the beans. The valve in our coffee bags allows the CO2 that seeps out of the beans to escape, while not allowing oxygen in. In the first days after roasting, so much CO2 escapes that it can affect the flavor. Coffee flavor is at its prime maybe 1-3 weeks after roasting. The older the coffee gets, the more porous it becomes. So if you're using the same grind size at one week after roasting versus two months later, the coffee will extract differently and taste differently.
Experiment with our coffee. Keep some of your coffee beans before your next coffee order. When the order arrives, open it and try it next to your older beans. If you're making a pour-over you'll see a difference in the bloom -- when you wet the grounds, there will be more bubbles (CO2 escaping) with the newer coffee. And you'll taste a richer flavor in the newer coffee. Just make sure to store your coffee away from heat, moisture, and light -- a simple jar in the cupboard is probably fine.
For more info, see here.