Actually the new recomendations are 4-6 months. There is a higher allergy link in children who start solids after 6 months and before 4 months. So the prime window is 4-6 months.
I have breastfed 5 of my 7 children. All started solids between 4-5 months. None have food allergies and all were ready. We dont do cereals we usually start with some homeade purees and by 6 months they eat table foods.
It is a personal decision. If you are ready at 4 months and baby is ready (good head control, thrust reflex is gone) then try. If you are not then wait. There is no harm in waiting either.