If you're allergic to a drug have a drug allergy can you outgrow it as you get older for instance i'm allergic to phenobarbital?

Maybe: There are some allergies that resolve as you grow older. For instance some people can get improvement in their response to certain medications as they get older, or further away from the initial exposure. This may be due to a calming of the inflammatory response as you age. However, if you were my patient i would not give you a medication that you were allergic to as the risk is too high.