Totally agree with Shelby!
My female year-olds get medium sized rats, the males are on small rats. Rule of thumb: Feed prey items equivalent or up to a MAXIMUM of 1.5 of the girth size of your ball python (depending on how often you feed.
The rats I'm feeding aren't the huge sewer rats that they have, I think they would be considered a medium rat. I'll try smaller food tho, I just hope it will be enough for him.