1985 Subaru GL doesn't run on 87 octane gasoline?

I am looking into buying a 1985 Subaru GL. I red reviews on this car and it seems very reliable and fuel efficient. The problem I see with the car is it runs on 89 or higher octane gasoline but will not run on 87 octane gasoline. Is this normal for this type of car? It has a 1.8 Litre engine and is carbureted. I cannot find an answer to this question. I want to know if this is normal for this car before I buy it. The owner of the vehicle told me that it only ran on 89 or higher octane.