We started at 5.5 months because my son didn't want to nurse in the mornings and wanted to eat a lot (more than my boobs can hold in the afternoon) in the afternoon but wouldn't take my pumped milk from a bottle, a cup, a dropper or an SNS. So, we would just mix my morning milk with a teaspoon of rice cereal in the afternoon and give it to him. Unless you have such a problem I don't see a reason to start any solids until 6 months though.