whoa.

Rat pups to a 2 1/2 year old ?

That seems way to small of a meal. Either the food is to small, or the snake has been somewhat stunted due to not feeding enough/big enough.

Can you post pictures of the snake and the set up ? Your temps ?

First you have to get your husbandry spot on. Heat, humidity and VERY importantly...privacy. Not to big of a space, not to open. Hides.
Then the snake should be left alone (no handling, other then emergency) UNTIL it eats. It needs to calm down after the stress of moving. A snake that doesn't feel safe, will not eat.

There is no problem feeding frozen thawed. I prefer it, for the safety of my snakes and to prevent internal/external parasites to be transferred to my snakes. Other people prefer live. But since you cannot get live, frozen thawed is not the problem. Make sure the meal is completely thawed out and WARM enough.

Offer the food, and then leave it with him in privacy (dark, in the hide) Don't watch.

But like others said, for now, give him at least a solid week without handling and in an enclosure with some privacy.

Please post pictures, rat pups is what I feed hatchlings (babies). He might be small, though, if the former owner didn't feed enough..