You can give rice cereal as long as you would like, however there are a few better options as first foods such as avocados, sweet potatoes and bananas, all which you can mash and puree yourself. All three have more nutritional value than rice cereal. Avocados is full of good fats for the baby's brain (which is crucial the first 2 years of life, 75% of the brain develops the first two yrs), sweet potatoes is full of beta carotene and Vitamin A and bananas is full of potassium. Then you can mix avocados with sweet potatoes (we loved sweet pocados!) and avocados with bananas for more nutrients and the fat. We put avocados in just about everything we made.
Avocado was my daughter's first food and she loved it and loves it to this day! A good brand of rice cereal is Happy Baby Bellies which has probiotics in them good for the digestive system and immune system. Be careful not to introduce grains too soon, then can end up with wheat or gluten allergies, study just published late this summer. Why the others are better choices. So stick with rice cereal and wait to introduce oats until 7-8m and other multi-grain cereals.
Good luck it is fun!
J. W. MPH
Wellness Educator/Lifestyle and Wellness Consultant