When is a good age to introduce cereal to babies?

It really depends on you whether you think your baby is ready for cereal (semi solid food). I introduced cereal mixed with bm or fm to my 4 mths old. Some parents prefer to wait till their baby is older like 6 mths and above as they want to feed their babies with bm exclusively. So is more of trial and error and knowing yourself and your baby as there isnt a really a good age.