I have yeast that is several years old and continue to use it pretty much as normal. I keep it in a sealed container in the freezer. It's possible that there is some deterioration with age, but I don't have a way of knowing how severe it is. My doughs seem to come out pretty much the same. The only yeast I throw away is fresh yeast, which lasts only a matter of days and doesn't freeze well.
You can also keep the unused yeast in the refrigerator for a reasonable time (a few weeks maybe?) but it will last a lot longer in the freezer. Just bring it out of the freezer when you are getting all your ingredients lined up and it will be ready to use once you start to make the dough.