Actually Rat pups for his size is perfect. Rat pups i feed are 25g each whcih is an adult mouse.
Next step up from rat pups is weaned rats and that is way to big for him now.
This is what i do with my snakes.
Hatchling- 100g Hopper mice or Fuzzy rat
101g-200g Large Hoppers-sm adults or Lg Fuzzy Rat
201-500g Sm adults - adults or Rat pup
500g- 1000g Adults- Retired Breeder Or wean rat
1001g+ 2-3 Breeder Mice or 1 Small rat