Can you post a picture...he's very light for his age, but he could just be small and be fine. The 12 hour bile thing isn't surprising, my dog does this as well. My dog isn't always hungry though and doesn't have EPI.
The dogs I know with EPI (when it hit) lost weight drastically, like 10 lbs in one month. Were always eating something (especially outside) and did have digestive issues. Another big sign is if the dog is highly irritable and reactive. This signals that something is wrong with the dog because it doesn't feel healthy and is worried the other dogs/people are going to "take care of it."