You can probably ignore the expiration date for the most part. All foods have to have an expiration date. In fact, go look at your bottles of water. THEY have an expiration date too thanks to the great state of New Jersey. Yes, bottled water has an expiration date, and it's only two years. Seriously.
Now that said, the limited amount of fats in the dry protein still have the potential to go rancid if they were stored in a warm environment or exposed to light. But if it was sealed (no oxygen), and in a cabinet (no light) then chances are you're good to go nd won't have any issues with the taste, either.