Few questions about my new corn

I received this beautiful corn snake from a co-worker the other day. She said she didn't take care of it as much as she should, so she just willingly gave him/her to me. I asked how old he is and she said he is at least 3 years old. I'm pretty sure they get pretty big at that age and this little guy isn't. With such a tiny figure, how big should the rodent be once i feed him? Here's a picture of him.

(and if you guys want to know, the temps are 85 hot side and 75 cold side, 56% humidity, he's currently in a 10 gallon which im going to switch out immediately to a 20 gallon once i get paid)

http://i46.tinypic.com/t6wj1u.jpg

Can't really tell how big he is from that photo. How much does he weigh in grams? That would be the easiest way to suggest a feeder size. My best guess from that pic would be mouse weanlings/small adults?

I just weighed him and he is 84 grams.

I'd stick him on about mice weanlings then to start him out

Here's how I feed my corn snakes:

1g - 15g = 1 pinky every 4-5 days
16g - 25g = 2 pinkies every 5-6 days
26g - 50g = 1 fuzzy every 5-6 days
51g - 90g = 1 hopper every 6-7 days
91g - 170g = 1 weaning every 7 days
170g+ = 1 adult mouse every 10-14 days (only weekly if you are breeding the snake)

Now, this can be adjusted. I have a 93g snow corn snake that's still a little small for weanling mice because she's so long. But I have a 150g bloodred who is really big but not long, so she might go up to adults a little sooner than 170g.

The best rule of thumb is to feed them no bigger than 1.5x the width of the biggest part of their bodies.