My severe food allergies started developing probably around 7 or 8 years ago. I'm 30 now. Before that, I just had OAS, though an OAS reaction did send me to the hospital in high school. (Where the doctor asked me if I had been punched in the face.)
For me, it seems to be part of my allergic development. Environmental allergies and asthma were diagnosed when I was 7, but given what we know about my medical history, they were probably around far before that. I have pretty severe asthma (uncontrolled on daily prednisone), nasty environmental allergies, and eczema. From what I have heard from others though, my eczema is mild - I only get it on my feet right now. I do take a pretty high dose of a PPI, but I didn't start until after the food allergies developed.
My brother is pretty much the opposite. He had pretty severe eczema, multiple food allergies, and asthma as a baby. He is pretty eczema free now, and has no food allergies (he is 19). He does have environmental allergies. He still has asthma, but doesn't even need a daily controller med any more, just a rescue inhaler very occasionally.