The reason flour is in paper bag (either 1kg/2lbs bags from supermarkets, or 25kg for bakeries) is to let it "breath": to get it oxidized. If you see an old (vintage) bag it's made of a net that lets a lot of air to get in. Today those bags are not used because it also allows bugs to get in.
When wheat grains are just milled, the flour is not good enough: it needs about 2 weeks of storage to get aged. But once aged, you don't need paper bags anymore.
Wheat grains have oils/fats inside. After 3 months of storage there will be too much rancid (oxidized, ¿stale?) oils in the flour and the taste won't be optimal. Trying to keep it in hermetic containers won't prolonge too much that time, as there's too much air in the flour.
Of course, modern industrial millers won't wait 2 weeks storing a product they could sell earlier: they add enzymes and chemicals to accelerate the process. As well as they'll add chemicals to postpone the "best before" date.
After that date, the flour will taste more rancid, and its gluten won't work as well.
To delay that rancid tasting, you might try to refrigerate the flour (IE: put it in the fridge) but 25kg are too much for a fridge. If you don't notice the taste at all, there's no problem eating it. The gluten won't work as well as when flour was "young", due to an excess of enzymatic activity. You'll notice this effect as the loaves won't rise as well, and the crumb will be denser and chewier. This could be solved adding very strong flour or wheat vital gluten (or just enjoying a denser bread).
Another problem you could get with long storage is some bugs appearing in your flour. There's no way to prevent them: their eggs are in the flour when you get it. But they usually appear only when it's hot, so you probably won't get them the next months (if you live in the northern hemisphere). In the summer that's one reason for me to convince my couple to store my flour in the fridge. An "old, wise trick" I was told was putting a leaf of laurel in the flour to avoid them. It never worked for me.