Can you have an anaphylaxis in adulthood (for example 40+) to something you ate before several times and never had a problem before? if yes, what are the most common allergens/foods for adult-onset anaphylaxis and what are the odds that it happens?

You can develop an allergy to something you have been exposed to at any time. An allergy is your immune system reacting to something it is exposed to and this can happen at any time and at any age. Anaphylaxis is a severe allergic reaction so it, too, can happen at any age to anything you are exposed to, including foods. Whatever is commonly eaten can become an allergen.