It is indeed possible to have food allergies occur at any age.
For some reason, the body starts to react to the substance and an allergy occurs. Sometimes medication can be a cause, the best way for exclusion. Is to do an food diary, and hopefully by keeping a list of what eaten and symptoms showing. The food causing symptoms or the allergy should be identifiable. Dairy products in particular are a leading cause of allergies, especially excema.
Thanks Kate, I have a feeling it is dairy that means no more chocolate for me :( x