Corns can get overweight with some specimens, and a lot of times, it can be very hard to come off. However, it still is a possibility for him to trim up.
While you may want him to slim down, you also want to not give him too little of food. How long is he? Each snake can differ in length, and if he is approaching two years old, and was large enough to be eating 1-2 adult mice a week, then he may have been powerfed, as well. Two year old corns, in my experience, rarely would be big enough to eat that much, if having a normal growth rate.
With all of that being said, what matters now is what will take place going forward. A lot of testing may ensue, to see how his weight trims up, if it does, on feedings you now will give him. If it were me, I would start out giving him one large adult mouse every 14 days, and then, from there, monitor and see how his weight does. I would not go smaller than a medium sized mouse, ever, at this point.
All of my biggest adult snakes are fed every 14 days, give or take, depending on the weight I see. Having never weighed a snake of mine ever, but just going by sight, and since their metabolism does slow down as they get age/reach adult size, I have found this schedule keeps them on a good weight and does not allow for obesity.
Good luck!!!
