It's actually longer than that and can be up to 3 weeks. Including your rooster once per week should maintain maximum fertility though.
The fertility doesn't change. Viability and hatchability does.
I try and set eggs that are a week old or less. If storing them longer there are methods which include turning your collected eggs and longer than 14 days includes a plastic wrap method.. the longer you store them the larger the air cell gets... the more evaporation there is... the smaller the chick.
They work quite often, hence the recommendation!
Your mileage will most likely vary... but for informational purposes, I have had pullets of the same breed from the same hatch and hatchery (or even my own) that take way longer to start laying than the first one. But hens are hatched will all the ovum they will ever produce already on board. If they start laying a little later... the first eggs are usually a little larger than the early layers... So it ends up washing out over time to be about the same...
