Me: can you develop allergies after childhood? Adolescence? Adulthood?

Yes. You can develop allergies at any age. Even in your elderly years, although this is less likely.
Anytime at all. Allergy onset is more common in childhood because that's when your immune system is naive and unprogrammed. Drug allergies commonly occur at anytime, as do food allergies to peanuts, tree nuts and seafood, and anaphylaxis to venom stings. Moving from one climate to another exposes you to a new set of pollens. Often allergy symptoms appear 2-3 years later.