Yellowing in paper is a combination of factors, primarily cellulose content, acidity, and exposure to light, heat, and air. Decent bond paper from the 1980s will generally look just fine if it's stored in a dry box. It has a low acidity and will normally have a higher dag content do will age more slowly.
Exposing it to sunlight and/or excessive heat will cause it to age. If it's high cellulose paper, like a newspaper, it will generally yellow quickly regardless of the storage because newspaper is cheap and acidic and not intended to last.
I'd like to know the brand. Almost 40 years old and not yellowed - that's amazing.