What you describe is certainly suggestive of some sort of pancreatic/gut dysfunction. There are a lot of things you might try first. I have a lot of experience with dogs who have the kinds of problems as you mention your dog has. Feel free to email me privately and I can ask you some specific questions and perhaps provide some things to try.
Doing the test will give you more information, but it is likely to result in your trying some of the things I and others might suggest in any case. So I might try some things before I shelled out the cash.
By the way, pancreas problems, just like other health issues, can surface at any age. They most commonly present in a dog over 3 years in my experience, but older dogs can begin to have trouble too as the pancreas looses the ability to consistently produce the correct kind and amount of enzymes necessary for digestion.