Self-diagnosis isn't easy. Allergies and asthma are different parts of the same health problem. Asthma attacks are caused by allergies. But once the bronchial tubes in the lungs become twitchy, even if all allergens were eliminated, you could still have asthma. If you don't have allergies as a child, you never will.
Allergies can start at any age.
However, allergies do tend to change over time. Children are more allergic to foods. Young adults can become allergic to pharmaceutical drugs, pollen and insect stings. If your information on allergies could use an update, talk to your family doctor. Specialists in allergies are called allergists.