I had a several of packages of old yeast, the freshest best by date 5 years old and some 6 or more years old. It was just stored at room temp and that could be 90°+ in summer because we don't run the air conditioning much in summer.
I followed a yeast freshness test from http://www.redstaryeast.com/lessons-yeast-baking/yeast-shelf-life-storage/yeast-freshness-test to see if my yeast had any life.
I used 1/2 cup very warm water (110-115°F) in a 1 cup measure. I used a thermometer to be sure. I added a 1 tsp. sugar and the dry yeast packet (from 2009) and stirred together. The mixture should begin to foam after 3-4 minutes and after 10 minutes it should double to the 1 cup mark. My yeast mixture came to about 3/4 cup after 10 minutes. I didn't think this was good enough, so I proofed another batch with older yeast (from 2008) to see if it was any good. It had about the same result, so I threw in another packet of yeast, hoping yeast of the same date/storage conditions would work in my recipe if it had double strength.
You must use your proofed yeast immediately, so I made a batch of sweet roll dough. The dough took way longer to raise before punching down, and much longer to double after making rolls, about 7 hours before I baked them. I should have put them in a warmer spot, I just covered them and left them at normal room temp (about 72°F). I tucked them next to a pot of beef stew I was cooking on the stove for about an hour to help it along.
Summary: It took a long time, but we finally had cinnamon rolls at 9:30 p.m.! And they were delicious! Maybe it was 'cause we had to wait so dang long for 'em. I won't bother with yeast older than 5 years. I suggest storing your yeast in refrigerator or freezer, I heard that can extend the yeast life that way. Or make cinnamon rolls more often!!!