I was very lucky with my boy. I got him as a 100ish gram baby that had only had live. I waited until the week I was picking him up at a reptile show and had a very current weight to order frozen rats.
Then about four days later I got an email saying my shipment would be delayed for 1 to 2 weeks as that size was out of stock. So not really thinking it would make a difference I brought home 2 frozen mice from work in the 12-15 gram range to hold me over... he ate instantly at his first feeding with me than again 5 days later. By then I had my rats in, and he at those too without hesitation. He's been going strong since, other than winter fasts that is.