What is his weight at now?
I took in a BP that was a 1/3 of where she needed to be. Now that she has put on all of the weight she needed, she is always looking for more. I'm not sure if they just feel the need to keep eating because they were under fed or its just their personalty.
I have never worked with Eastern Kings but I do have Cal Kings. I feed my adults 1 rat pup every 7 days and they seem to be doing well. My oldest is now over 20
I would say as long as he looks healthy, not skinny / not obese. He should be fine. Just keep him on a steady diet and get his weight every month for your records.
Good luck!