Rice cereal

Just had a visit with my doctor for my sons shots. He's in the 90th percentile for weight and height and his head is 100 percentile. Doctor said that a tiny bit of rice cereal was ok to give because he eats A LOT.... He's only 2 months old though. Anyone have experience with this? I'm a little weary on trying before 4 months but Doctor suggested it because he's so big for his age..... I dunno!