The AAP recommends not starting solids until at least 6 months. See these links for information on starting solids, and why it's best to wait until at least 6 months:
Why Delay Solids?
Solid food: Wait a Bit
When should my baby start solids?
Is my baby ready for solid foods?
How do we get started with solids?
Solid food: Best Delayed
And this one is especially fitting for your situation:
What if my 4-5 month old seems ready for solids?
All of the following organizations recommend that all babies be exclusively breastfed (no cereal, juice or any other foods) for the first 6 months of life (not the first 4-6 months):
World Health Organization, UNICEF, US Department of Health & Human Services, American Academy of Pediatrics, American Academy of Family Physicians, American Dietetic Association, Australian National Health and Medical Research Council, Royal Australian College of General Practitioners, Health CanadaHope this information helps! Let us know if you have any more questions or concerns.