Solids

My baby is almost 5 months old. Trying so hard to wait till 6 months to start solids. Doctor gave us a clear to try cereal because he would eat 36oz or more every 24hrs. He is a big baby. 19lbs and 28 inches.

I have read multiple articles about signs of readiness. He meets most of them except he can't sit unassisted yet. He just stares at our food and follows it as it goes to our mouth, he would try to grab anything and put it in his mouth, I tried having a spoon in front of him and he would open his mouth.

What do you guys think? He is already eating a little over max amount of milk for his age.

Suggestions?