Help!

So Carter was born at 31 weeks 1lb 12oz and 13in long. IUGR and pre eclampsia caused early delivery. He is now 4mths/2mths adjusted and is 6lbs 6oz and 19in long. Dr wants him to gain more weight and told us to up his feedings and add rice cereal to his bottles. I thought that he was a little too young for that, but I am not sure. He gets neosure 24 calorie formula already. Is that a good idea to add cereal so soon?