Can congestive heart failure occur to a 20 year old?

Yes: Yes , if the heart is damaged by viruses, drugs, valvular disease, trauma, chemotherapy, amyloid, etc.

It is uncommon: Congestive heart failure can arise at 20 years of age and even much younger as a consequence of congenital heart disease. It may also occur in a previously healthy individual following an infection in the heart known as myocarditis. There are rare degenerative conditions where heart failure presents in adolescence and young adulthood.