There are allergy tests for wheat, blood test for celiac (although it's not highly accurate). You won't get an accurate reading unless he eats wheat for a while before the tests. See a good allergist. If the problem is celiac, it's necessary to get a diagnosis to avoid cancer.
There are plenty of foods without wheat - meat, vegetables, fruits, milk, juice, rice, potatoes, salad, ... Stay away from sauces unless you cook them yourself using corn starch or tapioca. Tapioca and rice make good puddings. Don't buy the store ones. Avoid sandwiches, quick, processed foods, fast food restaurants. Check out some recipes on the many gluten free websites.
I can't eat processed foods or a lot of restaurant foods with sauces and seasonings. I have worse sensitivities than just wheat, but at least it's a sensitivity, not an allergy.