I consider an oil too old when the spec it was made for does not meet the spec I need. i.e. I wouldn't put a CG diesel oil in a motor that required a CJ-4. In that case, the CG oil is too old. Come to think of it, I have a quart of Quaker State oil in the old metal can, unopened, sitting on a shelf in the shop. I know it is from circa mid 1970's. I ought to open it up and send a sample in to my oil sample lab and see if it is still good. My bet, it is. Won't get put in anything I run now anyway. Plastic containers, it might be another story.