Here're a few 'clues' to whether she's ready:
- can she sit upright steadily already?
- does she show interest in the food that you eat?
- does she seem to be always hungry?
If the answer is 'yes' to all the above, then she's probably ready. Although I would think there's no harm waiting another month till she's 6 months old to start. She'll probably push out the cereal with her tongue the first few times you try to feed her. And you'd only be able to feed her with a few spoonfuls at first. It takes practice and for her to get used to the taste of new food and feeding method, so the portion will only slowly and gradually increase. HTH!