No one in my family had/has peanut allergies but I do. No one in my granddaughter's family has peanut allergies but she does. Her allergies were discovered when she was a few months old. Because she was not responding well to formula her pediatrician tested her for several common allergies. Milk protein, soy, and peanuts all were positive. She's now 10 and still tests positive for peanuts. She's outgrown the milk protein and soy. It is rare to outgrow a peanut allergy.
I don't knew when I developed my allergy to peanuts. I was tested in my 20's because of digestive complaints. The allergists over the years have said that peanuts is one of the foods that is commonly an allergen now although it wasn't in the past. Knowing that p eanuts are not a tree nut helps us understand better about how to treat it. I highly recommend that you not give your son peanut butter until later. I think that you can use other nut butters but you should ask the pediatrician first.
Two years ago there were 6 children in my granddaughter's grade school, with a population around 300, who had an epi-pen at school because of peanut allergies. When a child has a peanut allergy, the doctor recommends having an epi-pen available at all times.
In my opinion, starting peanut butter early is not worth the risk of creating a peanut allergy. True, the chances of doing so are slim but the consequences are serious. What's another 8 months vs. a lifetime.