We started two weeks ago when DS was just over 5 months but was recommended to start because DS is so big and is likely to be needing more iron and zinc now. Behaviourally he also seemed very ready (once he even grabbed DH face so he could try and get the food that had just gone into DH's mouth!). From what I understand the reason the age is set at 6 months is because starting early may increase the risk of food allergies. We are being very careful to not allow contact with any usual suspects (wheat, milk, honey etc) and don't have food allergies in the family. Perhaps check with your Dr or Child Health Nurse about what they recommend specifically for you.
HTH.