Every baby is different and when you start to feed them more depends on them. The general rule that most doctors will tell you ( I have had 5 different doctors tell me this not including the ladies at the wic office) They usually say to introduce rice cereal to them at 6 mos. However you can tell if your baby is ready by little cues, like them smacking their lips when they see you eat. Every baby is a little different. The reason they tell you to wait that long to introduce foods is to help prevent future food allergy problems.
Think of it this way, when your baby is born and for the first few months of life their stomach isn't developed enough to handle the digestion of our more complex foods, therefore because their stomach is not developed enough their body treats the food as if it were a foreign substance and will build antibodies towards it. When an allergic reaction does occur it is the bodies immune system reacting as if something is bad and tries to repel it or attack it. So if you give your baby foods before their stomach is ready or developed enough you could potentially increase their risks for having allergies later in life. Not every baby is going to develop allergies and you breastfeeding will actually help to reduce that risk. But every baby is different and their stomach may be ready sooner than others, My mom fed us food starting at 2 mos. and by 9 mos we were already eating some table foods, including cottage cheese, spaghettios, and several others. She pushed us to achieve everything early and you know what I am allergic to everything!!!!
I'm allergic to all fresh fruits and Veggies, even some cooked, Im allergic to milk, wheat, soy, peanuts, eggs. What is left to eat then. Not much, and you know what my allergies never developed enough until I was older. They slowly get worse. That is not to mention the things I am allergic to outside. Someday I will be bubble girl.
Anyhow, the point is follow your instincts, you will know when your baby is ready.
By the way KUDOS to breastfeeding your baby keep up the good work.