How long do you keep your grains and flours? And at what point do you toss them and start over?

I used to use "Flour Girls" whole wheat flour from the northwest. It was lighter, and the best thing was that it didn't become rancid even for years. (I found a years-old bag in back of some other items in a corner pantry, and it was still good!) As for AP flour, I don't use much but I keep it around anyway, in a sealed container in a dark cupboard. Same goes for grains. I throw away any brown rice or other whole grain that smells rancid, but we usually eat it up before then.

Hi! I don't worry too much about all-purpose, since I go through it so quickly—but if it's a whole-grain flour I only use occasionally (whole-grain flours turn rancid sooner), I'll keep it in the freezer to preserve its shelf-life.

I come at the question from the opposite end, sort of. I buy all mine in bulk, and in quantities that I know I will use up within a couple of weeks. I load them into my own paper bags, then transfer them to glass jars at home. They are all stored out of direct heat and sunlight, both of which can cause them to degrade faster. Using them up has never been a problem.

Summer of Eggplant - have a look at this site (example: rec durations for keeping white & ww flour at room, fridge & freezer temps)
https://www.stilltasty.com/searchitems/search