Every few years there are new recommendations. Some cultures start solid food almost right away. When I was practicing in San Luis Obispo, I saw many families of the Oaxaca culture from Mexico. They would chew food to feed to their infants. I also know some Indian families who give their very young children curry. They all do just fine. Kids are really good at taking the right food they need to grow if you give them a good, healthy variety. We are blessed in America to have enough calories around for our children to grow.