Breast milk is all your baby will need until at least 4 months of age. There does come a time, when breast milk will no longer supply all of your baby’s nutrition needs. Full term babies will start to require iron from other sources by 6 - 9 months of age.
Some babies that aren’t started on solid foods by the age of 9 - 12 months may have a great level of difficulty accepting solid foods. It’s actually a developmental milestone when your child starts solid foods - as he is now growing up.