When Can I Introduce Peanut Butter?

[Ambah]

I have heard you should wait until at least 2 yrs to give them peanut butter, and 5 years if there is a history of allergy.
I tried Aidyn just before he was 2, and he was allergic - not anaphylactic, but had he eaten a whole sanwich then he would have been.
ETA - bear in mind that if they are allergic they wont react on their first exposure (unless they have been exposed to it in the womb or through BM perhaps), it will be subsequent exposure where the allergic reactions will begin)