There are two things in life: facts and opinions. I used to take it as a fact that the age of yeast is critical; that it is a fact that reused yeast that is over a year old is worthless. I now wonder whether this should be moved over to the realm of opinion.
I recently brewed a blueberry wheat with year old yeast (actually 15 month of yeast; 1056 used previously in an IPA on or about June 2011, which has been sitting in the fridge since that time). I used a 2 liter starter and shook it around when I was able to (my version of a stir-plate) and 2 days later, I pitched that yeast into the blueberry wheat. Within a 6 hour period, there were bubbles. I recently transferred it to the secondary and took a gravity reading. In a 2-week period, my gravity went from a 1.050 down to a 1.004. And it tasted good: a little stronger and drier than I wanted, but good nevertheless.
So, am I onto something? Is the age of yeast just a preferential thing relegated to the realm of opinion, such as Obama v. Romney, Tastes Great v. Less Filling and the proper method of installing toilet paper? Or, is my experience an aberration?