I was diagnosed with a cashew nut allergy as a small child, will i still be allergic 20 years later?

Probably: Only about 10% or less of people with nut allergy actually "out grow" it. If the reaction was very severe, it is less likely. Since there is a small chance of not being allergic, an allergy skin test and blood test to cashew would be one way to assess if sensitivity is still present. An allergist can assist in the diagnosis and interpretation of these tests.