For what it's worth, my 3' female snow corn usually gets fed 2 pretty large adult mice every couple of weeks. I haven't switched her to jumbo mice (RodentPro's jumbo mice are really pretty big) because she seems to have some difficulty with them and takes her much longer to eat one...just can't seem to comfortably get her mouth around it. However, my 4' snow male eats a couple of jumbo mice every two weeks with no difficulty. IMO, it probably wouldn't hurt to use somewhat bigger prey, but 3 feet for a 2 year old doesn't sound like it's been grown too quickly to me. Another thing I'd like to mention is that even with my male corn, his head looks small to me compared to his girth - though it's in proper proportion to his size...for a corn snake. I'm used to boas and pythons, which generally have much larger heads on snakes of the same length as my corns.
Just a thought.
Raven