peanut butter is considered ok from 6 months unless there is a family history of allergic diseases. DD had it from about 1 year and ds had it from 9 months. From Babycentre website:
Nuts
It's true that you shouldn't give whole nuts to children who are under five years old, because of the risk of choking. But nut butters and ground nuts are fine for babies over six months old and children who do not have a family history of allergies.
Serious allergies to nuts and nut products and some seeds affect less than one per cent of the population. Your baby may be at higher risk if you, your baby's father, brothers or sisters have certain allergic conditions such as hayfever, asthma and/or eczema.
If your baby is in this higher-risk group, avoid eating peanuts and peanut products while pregnant, during breastfeeding and during the introduction of solid foods. Until your child is at least three years old, peanuts and peanut products should be avoided.
If you think your child might be allergic to peanuts, contact your GP who can arrange for your baby to see an allergy specialist.
If you do not have a history of allergy in the family, you can give your baby ground nuts and nut spreads, including peanut butter, from six months.