if you have no family history of allergies then peanut butter can be introduced from 6 months. DD had it around 1 year and ds had it from about 9 months. The guidance from the Government and Food Standards Agency was also changed in August 2009 after studies showed no clear evidence that eating or not eating peanuts (or foods containing peanuts) during pregnancy, breastfeeding or early childhood has any effect on the chances of a child developing a peanut allergy.
This is from the babycentre website:
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.
The Department of Health says that if you or your partner has a history of allergies, you may wish to consider avoiding peanuts during pregnancy and breastfeeding, and not feed your child peanuts for her first three years. However, the Food Standards Agency has said this advice should be withdrawn, because there's not enough evidence to support it.
If you have a family history of allergy, seek your GP's advice about weaning. You might also ask her to arrange for your baby to see an allergy specialist.