Your account must be at least a year old, for there is surely no greater responsibility than proper use of post ratings.
I can rate posts, and my account is far younger than a year old... I was able to as soon as I had something like ten renown, or maybe a certain number of posts. (Now, my ratings don't actually affect the renown and infamy of the people to whom I apply it, but at least I can increment that little number over the post.)
