I definitely like to wait until 6 months or as close to that as possible since the gut doesn't close until 4-6 months (and best to be safe). Of course thing can change with reflux issues, etc. And I don't do any grains until 8-9 months (and then oatmeal) - IMO rice cereal has no real nutritional value and prefer to start with real foods - avocado, banana, sweet potato, egg yolk, etc.