plsql procedure that will detele rows : I have a table: USERS, with fields: username,fname, lname, age

I need to create procedure that will delete username from parameter, if the age if less than 18
I did some code, but it won't work:

    create procedure delete_user(username in varchar2)
    as    
    begin
    if exists (delete from username  where age < 18);
    
        dmbs_output.put_line(username);
    end;
    exec detele_user('mrgreen');