Malted grains are generally good if stored in a cool dry place for a year or so. Sounds like you have the "dry" covered but the "cool" maybe a challenge. I agree with IffyG, taste it. Malted grains can oxidize faster in warmer temperatures and they will take on a "stale" or papery character. Is this base malt or specialty malts?? Darker malts can go a longer time and show lesser effects of oxidation.