To minimize the risk of allergy, wait until he's 2 yrs old. Especially if food allergies are in the baby's birth family. PB is also a choking hazard for children under 2 yrs old.
That said, I found it difficult to keep my youngest daughter from avoiding peanut butter once she turned 15 months old because she would literally "steal" her older sisters sandwiches. When we made sure she had no allergic reactions (I'm allergic to nuts and peanut butter) we decided she could have it occasionally and in small amounts.
ETA: It's good to remember that if a child is allergic to nuts or peanuts or any food that causes him to have an allergic reaction, the reaction will get worse with each new exposure. A nut allergy can at least be outgrown, but introducing a food such as this too early can be a serious life-threatening issue, despite what a pp said about giving her child adult foods before 6 months old.
An allergic reaction could be:
*fever
*digestive problems
*diarrhea
*hives
*vomiting
*rash
*cradle cap
*dull hair and skin
*listless behavior
*anaphylactic shock where the throat swells up and the child can't breathe
*choking
*itching
*nausea
*headaches
*body aches
*mood changes
BTW Chocolate can cause SERIOUS digestive problems in children under 2 yrs old... extreme diarrhea or extreme constipation. There's a reason the AAP recommends waiting on certain foods, and I'd follow the AAP before following what WIC suggests. WIC is not nutritionists and should definitely not be telling you when to start your child on particular foods. They're not qualified. I've lived my entire life with allergies to certain foods, so I know the dangers. Please don't listen to anyone who would tell you that allergies aren't something to worry about, especially with peanut butter.