Hi Chris,
I was 50 at time of Whipple surgery. On Johns Hopkins discussion board, there are several patients in the 40's who have had the surgery. You may want to check that board out as well as this one.
Your surgical team should give you advice for post operative diet. Most likely you will be referred to a Nutritionist for advice as well.
For the first few weeks following surgery, I ate frequent small meals, low fat, low sugar. Had to make myself do it because I didn't have much of an appetite. I believe this is common following Whipple surgery. But the good news is, your appetite will return with time. You may find you cannot tolerate food post surgery that you enjoyed with no problem before surgery. It really is trial and error for the most part. The key is to get those calories in you to prevent weight loss, which is also common post surgery. Eat even if you don't want it.
I was a l sensitive to spices (even black pepper) for a while and high sugar foods caused what I found out were blood sugar spikes.
If your Doctor doesn't bring it up, be sure to ask about Pancreatic Enzymes. Depending on how much and what part of the pancreas is removed, will determine whether you need them to help digest food. The Doctors didn't think I would need them. I struggled for six months trying to find the right combination of foods to control symptoms before enzymes were prescribed. Once I started taking enzymes, I could eat pretty much anything I wanted and stopped losing weight.
The PANCAN (www.pancan.org)site has good information on diet for pancreatic cancer patients as well as other information you may find useful.
Best wishes for a good outcome from your surgery and a quick recovery.