I do agree with most points on this poster, however oatmeal/quinoa cereal doesn't help them sleep through the night either.....
Anyway studies show that parents should wait until 6 months to introduce any kind of solids/purees/cereals. Before then, the baby has a higher chance of "sucking" the food rather than eating it, and can aspirate among other things.

6 months I started giving my little cousin food I was constantly worried shed get choked so I'd cut it into really small pieces

good question I want to know too