I had some peanut butter out of a 3 year old jar of opened JIF Creamy that was stored in a kitchen cabinet. Other than tasting stale, it seemed OK to me. I did not get ill.

According to Still Tasty.

"An unopened jar can be stored for up to 2 years.
An opened jar can be stored for 3 months in the refrigerator or 3-4 months after pantry storage.

Storage time shown is for best quality only — after that, the peanut butter's texture, color or flavor may change, but in most cases, it will still be safe to consume if it has been stored properly."