Just came across this in an article in the paper today.

"Meanwhile, new evidence has even called into question the standard advice that young children be deprived of potentially allergenic foods for their first years, based on the belief that early exposure may lead to allergy later. A British study compared about 5,000 Jewish children in the U.K. who rarely ate peanuts as babies or toddlers and a similar number in Israel who started consuming peanut products early on. The British, peanut-avoiding children were 10 times more likely to develop peanut allergies, according to a paper last November in the Journal of Allergy and Clinical Immunology."

Food for thought.
My kids had peanut butter from about 11-12 months on, and we haven't had issues, but then, there is no family history of any type of food allergy either. You can talk to your GP and see what he/she recommends.