I've used grain that is well over a year old without any trouble, I usually get it whole and crush it myself though. Also, I've used a smackpack that was 39 months past is use by date with no ill effects. The older theyeast gets the longer you need to plan to step up a starter. It took the yeast about 10 days to swell the smackpack, then I made a starter from there. The beer was fine.