Four months old it should be easily eating a single rat pup every 5 - 7 days. Personally, I go every 5 days until they get to 250 - 300 grams. Then I move to every 7 days. You should be feeding 10 - 15% of it's body weight. If you don't have one, invest in a digital scale to weigh your snake. You can get one at Walmart for less than $20.00.