I have a box of Krusteze that I know is at least 3 years old. Maybe 4. We ate some of it last summer. Five of us. Nobody sick, however, I keep it in the deep freeze at below 0F temp.

At home, I make scratch pancakes. I only use the mix when camping, so a box lasts a LONG time.

And, keeping flour, grains, cereal, etc in plastic bags or things with lids will not necessarily keep the weevils out. The EGGS were probably already in there. When you purchase the stuff, put it in the deep freeze below 0 F for a week or two, THEN put in in the bag, bin with lid, etc.
The freezing kills all the active weevil eggs that might have been in it.

All this stuff keeps fresher and much longer in the freezer anyway, if you have room to store it there.