2 month checkup

So LO was at 2 month checkup yesterday and his pediatrician told me to start giving solid at 4 month and I told him aren’t solid starts at 6 month but he told me they recommend at 4 month (and I think that is early).Did any other pediatrician told any mom that?

Also his head circumference (I think this is right word 🤷🏻‍♀️) is 38.5 cm - 45 percentile / so I don’t understand that is it good or bad, because his height and weight are above 85%.His doc told me he is growing good but I’m worried about everything.

And he is formula fed.