PL SQL Programming Oracle PLSQL Tutorial

There is no forward declaration.
Multiple declarations are supported in PL/SQL, as shown here:

SQL> declare
  2      --v1, v2 NUMBER; -- INVALID
  3      -- VALID
  4      v1 NUMBER;
  5      v2 NUMBER;
  6  begin
  7      NULL;
  8  end;
  9  /
PL/SQL procedure successfully completed.