<<Disclaimer: Verify this information before applying it to your situation.>>
 
People use the word allergy to describe all sorts of reactions to
foods, such as rashes, diarrhea, nausea, etc.
 
If someone is truly allergic to wheat or is a celiac (not the same
thing) he would not "outgrow" the condition.
 
My impression is that people who are still allergic to a food or who
have a mild celiac enteropathy mentally adjust to the tired feeling and
various other symptoms especially gastrointestinal.
 
This usegroup is filled with people who were diagnosed as having
irritable colons or other wastebasket diagnoses before establishing a
precise cause for their woes.
 
Until someone is really miserable with the symptoms, he can "adjust" to
this for a very long time.
 
The only way to prove that you have a food intolerance is by small bowel
biopsy and/or serum testing for antibodies.
 
Anyhow, why try to prove something to someone who doesn't want to listen
and has a strong investment in proving you wrong?