The Government's eating well site has a weaning suggestion and says peanuts can be given from 6 months:
Nuts and seeds ? including peanuts, peanut butter and other nut spreads. Peanuts can be given from six months old, if you always crush or flake them. Don't give whole peanuts or any type of whole nuts to children under five years old because they could cause choking.
It is only children in the higher-risk categories who are recommended to wait until 3 years:
Nut allergy
Some people are allergic to nuts or seeds. Peanut allergy appears to be increasing among children, although it's still uncommon. We don't yet know why it's on the increase.
The children who face the highest risk of nut allergy are those with parents, brothers or sisters who suffer from certain allergic conditions, such as asthma, eczema, or hayfever.
If your baby is in this higher-risk group, it would be sensible to:
avoid eating peanuts or peanut products when you're breastfeeding
avoid giving peanuts, foods containing peanuts (such as peanut butter) or unrefined cold-pressed groundnut (peanut) oil, until the child is at least three years old
always read ingredients lists carefully and, if you're in doubt, avoid the product