I’m about to change oil (and filter, always) in my '98 accord with 125K. I have some quarts of oil that must be 5 years old, never used, just been sitting that long. Any reason I shouldn’t use this oil?
If it matches the recommended weight, check your owners manual, then there is no reason to not use it.
Thanks. Yes, it is the proper weight for this car. I personally can’t imagine why it would ‘break down’ just sitting in the can (well, plastic quart container) but wanted to check. After all, it’s only saving $10 or so. If there is any doubt, I wouldn’t do it.
I don’t think there will be a problem as long as the container is sealed and it is the correct or better service rating for your car (the “SJ” or “SH” rating, for example). 20-year old oil I would worry about.
If you think about it, the oil was in the ground for millions of years so what’s another 5 years! 
Since your car is older than the oil you don’t even have to worry about the API rating. Yep, go ahead and use it. No worries.
Last summer I ran across some OLD OIL…IN CANS…remember those. Just two. I used them…Never had a problem.
So long as it hasn’t been opened (and possibly contaminated or oxidized) and is the correct weight and is the correct API rating (SE, SF, etc.) go ahead and use the old oil.
Now, gasoline is another matter. If it has been sitting for more than 2 or 3 months, especially without stabilizer treatment, it’s probably oxidized to the point of being loaded with gums and varnishes, and will clog your fuel system if used. My system is to take whatever (straight gas) I haven’t used in the snowblower or chainsaw for a couple of months and dump it in the car to use it up, and get fresh gas for the gas can.
I have a friend who has a gas-powered generator last fired up about 5 or 6 years ago, and never “put in storage”. The recoil starter won’t even turn it over and the tank is full of gas dating back to Bill’s administration. She’s asked me to try to fix it – I dread what I’m going to find.