I am allergic to shellfish, but not all shellfish. Only crustaceans, not mollusks. (Can't eat shrimp, lobster, etc.) The first time I had a reaction I was 10 and eating out with a friend's family. I tried to explain what was happening, but the mom thought I had indigestion or something. In reality, I was having chest pains.

No one expects a 10 y.o. to have chest pains. I got blisters inside my mouth and had trouble breathing, but not enough for her to notice.
A few years later, I ate shrimp again and the reaction was much worse. Chest pains again, throat swelled shut, blisters in mouth, puffy lips, whites of my eyes turned yellow, etc. No one in my family (and I have a huge family) has this allergy...just me. After that, no more shrimp for me. A year or so later, my parents were boiling shrimp and I had a reaction just from being close to fresh shrimp being boiled. In high school, I took a small bite of lobster and started to have a reaction, but my BF's mom gave me a fistful of Benadryl and nipped the reaction in the bud. Never again.
If I eat in a restaurant where a fair amount of seafood is served, I tell them about the allergy and they make certain they use a fresh pan, oil, etc. You learn to be careful about sauces. Glucosamine is derived from shellfish, so I can't take that. I carry an EpiPen just in case. I never buy seafood that has been next to crustaceans in the seafood dept.
Truly, the peanut allergy will be harder to manage because it's harder to spot peanut products than shellfish products. And peanut products are more commonly added to food. Good luck.