I've always felt strongly about this topic. DS1 and DD started baby food (veggies) just shy of 6 months old and that's our plan for DS2. I think it's important that they show all the readiness signs, including being able to sit up as you mentioned.
My DS didn't show signs of being ready until he was just shy of 5 months. I waited til he showed the signs. We're two weeks into solids and he's still not very good at it, so I may in fact have started him too soon.
Pedi said it was ok, so we gave it a shot. She was not into it at all. She recently started showing the signs that she might be ready, but I think after all the research that I might wait till 6 months.
Re: Whose 4 month old is NOT ready for cereal?
My three little ones
mine was not... but today... i think he is...