My allergist told me you can develop any allergy at any time. I had a milk allergy as a baby that I outgrew, then in my teens was diagnosed with allergies to wheat, soy, and peanuts. Then in my 20's I had a scratch test done again and came up positive to shellfish and tree nuts, in addition to the ones diagnosed in my 20's. I have read that allergies are tricky and can come out of the blue.

its the way allergic conditions co-exist, this link might help, its UK based but its similar for those in other countries like USA and Canada http://www.londonallergy.com/the-allergic-march/

Sounds like the atopic march, a pattern that food allergic children follow. food allergy, eczema, and environmental allergies start developing. my son has terrible eczema which eased at 5, but his environmental allergies really kicked in. Has a list of food allergies. some he grew out of and some he did not. This is apparently typical of the atopic march.

My step mom was never allergic to anything and developed a shrimp allergy later in life and her reactions get worse every time. She was finally told to stop eating it all together and carry epi pens

Allergies are 'fluid' and do change. For those on the atopic march as infants/ children, they tend to develop environmental allergies, as they grow older. He grew out of some allergies, but added some more when he reached 5, at the time as his skin improved his tree pollen, hay fever allergies got much worse. Fitting with the atopic march. As an adult he has a smaller list of food allergies but is allergic to all environmental allergies.