I had ashma and allergies when until i was 9ish then it seemed to go away. is it possible that ashma and allergies change or come back 20 years later?

Yes: Both asthma and allergies have a genetic component that does not change.The combination of triggers during your growing years may have become less sensitive as you became older.However, at some point, a combination of triggers could break though and produce a return of symptoms.

Absolutely : Asthma & allergies never truly go away, although some people's symptoms may become subclinical over time. As the disease becomes less prominent, their symptomatic episodes may become less and less frequent, and they may be able to wean off medications. However, the underlying tendency to "over-react" to allergens or irritants persists. Sometimes exercise-induced symptoms appear later in life.