How many oz does your 5 month take a day?

My little boy is almost 5 months and consistently taking 34 oz of formula a day now. I have tried capping him at 32 oz per the aap recommendations but he screams for more. Does anyone know why there is a 32 oz limit? I had wanted to wait to 6 mo to start solids but I guess I may have to start sooner? My pediatrician gave me a pamphlet at his 4 mo appt and said I could start between 4-6 mo but that is a wide range and I’m feeling a bit lost but afraid of over feeding since he spits up a lot. He is ~16 lbs.