as icemaiden has just said there are good reasons for the age being changed to 6mths, they now know more than they did before!
Being hungry is not actually a sign to start weaning, you can just increase the milk if what you are giving is not enough.
Weaning is a learning process, to discover the tastes and textures of food, its not just to fill your baby up, the signs that your baby is ready to start weaning are that they can sit up well enough to be able to grab food themselves and attempt to put it in their mouth, that way there is no need for any purees, which makes it a lot easier for you, as you can give your baby small pieces of soft food to feed themselves and make a mess with! that way they can discover the different tastes and textures and they learn hand eye coordination as well as developing their tongue muscles for speech.plus they love it and are less fussy later on! i'm sure the baby rice you have given will do no harm but your baby probably doesnt need it yet. i hope that helps.