I used to make bread quite frequently, but since we moved house and DS2 was born last December, I realise that I haven't made any for about a year. (this year has flown! ) I just checked my cupboard and all my bread flours are badly out of date - the 'newest' was sell-by last January. That's a sealed packet, too. So are they really out of date? Stale-tasting? Weevil-ridden? What happens to old flour? Is it a gluten issue, maybe? In the interests of economy, I'd hate to chuck it all out, but in the interests of time-economy (DS2 doesn't really allow me much bread-making time) I don't want to spend ages making bread that doesn't do what it's supposed to do.
Check for weevils, obviously, but there's little else that can happen to (white?) flour in a sealed packet. Brown flour contains the oil of the wheatgerm etc., which can go rancid and therefore bring down storage time, but white flour is a lot more sterile and keeps very happily in dry conditions for yonks. I'd cook it up and judge by the taste.