Oh, my mistake

Where do you buy your rats?

If you have a local pet store close by drop in and ask to see the feeder rats.... If they dont have feeders check out the pet rats.
Then compare the size of the rat to the girth of your snake. And then just ask if it's a pup or weaned. That should give you a general idea

I dont order off feeder sites so i dont have first hand expirence, mabey some one eles here does

Chris