Yes, you can use flour 2 years out of date, as long as the flour smells neutral and as long as the flour has no signs of pests, moisture or mold.
Although whole grain flour and self rising flour is best not used after 2 years out of date.
Whole wheat flours and nut flours often go rancid more quickly due to their natural oils and self rising flour loses it's leavening power, so these flours are best discarded if they are out of date, especially 2 years out of date.
You should also inspect the flour for any pests, by pouring a small amount of flour onto a plate and look for tiny insects, like web like clumps or weevils.
If there are just a few weevils in the flour and it's not infested you can safely use the rest of the flour as long as you sift it.
Also fresh flour has a neutral or mildly sweet scent to it and if the flour has any musty, sour or like old paint smell, then the flour has gone rancid and should be thrown out.
You can also try baking a small, simple batch of something like a basic flatbread for example to test if the flavor is not compromised.
To stockpile flour you can stockpile the flour by storing the large amounts of flour in food safe 5 gallon plastic buckets that have a fitted gamma seal lid or even an 18 quart Cambro container.
Before storing the flour in the 5 gallon food safe plastic buckets, freeze the flour first to kill any weevil eggs.
Once you have the flour in the 5 gallon food safe plastic buckets with gamma seal lids, store the 5 gallon buckets of flour in a cool, dry and dark location away from any strong odors.
You can also buy flour containers and flour bins on Amazon, although the 5 gallon food safe buckets with gamma seal lids work great.
To keep bugs out of your flour, freeze the new flour for 3 to 4 days and then transfer the flour to an airtight container and then add natural bug repellents to the flour like bay leaves.
Eggs for the bugs can be present when you buy the flour and so you need to eliminate these eggs that could be present by freezing the flour.
Immediately place any newly purchased flour in your freezer for 3 days to 4 days or even 7 days.
And the freezing temperatures will permanently neutralize and kill any unhatched bug eggs or larvae that can be in the flour.
And never leave your flour in the original paper bag that the flour comes in, as bugs can easily chew through the paper bag.
Instead transfer the flour from the paper bag, into a glass jar like glass mason jars or even heavy duty plastic containers that have silicone seals.
Dropping 1 or 2 whole bay leaves or even a few cinnamon sticks directly into the flour container can also help keep bugs out of your flour as the scent of the whole bay leaves or cinnamon sticks act as good natural deterrents for bugs like weevils and other pantry pests that can be in your flour.
And if you buy your flour in bulk, you can also use a vacuum sealing system or even an automatic jar sealer to extract all of the air.
And then vacuum sealed flour can remain free of bugs and even fresh for up to 2 years time.
Then when you're ready to bake or use the flour, take your flour out and allow your flour to come completely to room temperature while the container also remains sealed.
This will prevent any moisture and condensation from ruining the flours texture.
Having some bugs in your flour can be normal and does not mean you need to throw the flour out.
Although if the flour is heavily infested with bugs and you can't sift all the bugs out of the flour then it should be thrown out.
If the flour is heavily infested, then the flour is likely contaminated, but if it's just a few bugs then the flour is often safe to use.