Peanut butter

My little one’s doc said our guy’s ready for some solids. Rice cereal, oatmeal and purées.. I think based on some research I’m going to wait a little but until he can sit unsupported, he’s 4.5 months right now.

But the pedi also said we could try to introduce peanut butter early since there are studies that earlier introductions to foods can help prevent allergies. He said we can start by putting a tiny bit in his leg, see if he reacts. If not try a tiny bit in his lip etc .. has anyone done this?