At that age you just need to eyeball it and feed a prey slightly smaller to equal the girth size (widest part of your BP's body) you can feed him every 5 to 7 days.
As he will grow his metabolism will change so will the way you will feed him but for now that is what will work.
Once he will be an adult assuming it is a male he will not require more than 2 to 3 mice per feeding or a small rat in the 55/65 grams range once a week (at that point you no longer go by girth size)
Congrats on the feeding :gj: