Yeah-- I wonder, too, if adult-onset allergies are somehow more.... mutable in some ways, and less so in others. Just-- different.
It seems like the conventional wisdom is that many childhood food allergies are HIGHLY mutable with external pressors of various kinds (which is what immunotherapy is based around) and that the adult versions tend to be less so in terms of MOVING the person's response from intolerant to tolerant... on the other hand, adult threshold doses seem to be more mutable in some cases, and honestly, less predictably so.
Kids tend to have relatively stable sensitivity to allergens, and as they age into adolescence and young adulthood, something happens that destabilizes that-- which is where you get those very sad and scary anecdotes about teens or young adults being COMPLETELY caught by surprise when they anaphylax out of the blue to something that has "always been fine before."
Adults who have adult-onset food allergies have just always had that be so-- most people with adult-onset, there's this weird opening phase of things where even stuff you ARE NOT allergic to, you react to-- it's like your immune system views everything with some degree of suspicion, and some days, some things... more than others. But unpredictable.
The allergen itself seems to matter less than the age of onset in some strange way, though the 'persistant' allergens tend to be of the "adult-type" right from the get-go in some people who are likely to have them be life-long. Peanut, nuts, shellfish... though even there, people with them tend to age into that adult presentation where sensitivity can vary wildly, symptoms can vary wildly, etc.