You can unfortunatly never 'out grow' an allergy. The immune system has a great memory and will react forever. You can give immunization shots, but even those don't make the allergy go away and aren't appropriate for food allergies.
"Food allergen testing
The history and clinical signs of cutaneous adverse food reactions are often identical to those of atopic dermatitis, and a hypoallergenic food
trial is necessary to distinguish between the two diseases. In addition, some dogs with atopic dermatitis have concurrent cutaneous adverse
food reactions. Most laboratories offer food allergen panels for serum testing despite the fact that studies suggest allergen-specific IgE serology is not helpful in diagnosing cutaneous adverse food reactions.6,7 These tests also do not appear to be of value in determining which foods to avoid in a food trial. Thus, they should not be used in place of appropriate hypoallergenic elimination diet food trials."
http://www.alerchek.com/march_allergy_hiller_02.pdf
There is a great booklet, 'Allergy Problems', by Monica Segal that could guide you threw an elimination diet if you choose to go that route.
http://www.monicasegal.com/catalog/product.php?cPath=25_26&products_id=72
Sometimes with very sensitive dogs and commercial dog foods they can react to something so seemingly innocent as the source of calcium. Homemade diets where you control all ingredients often work best for these dogs.
You could also be dealing with environmental triggers and that would compound your issue. Why do you think it is only food and not environmental? Have you ever tried a commercial hydrolyzed diet?