How to check date is valid or not using oracle

create or replace FUNCTION IS_VALIDDATE(v_date IN VARCHAR2) RETURN NUMBER IS
    v_date1 DATE;
BEGIN

    SELECT TO_DATE(substr(v_date,0,10),'mm/dd/yyyy') INTO v_date1 FROM DUAL;
        RETURN 1;
    Exception WHEN Others THEN
        RETURN 0;
END;

to check---

select IS_VALIDDATE('04/21/2015') as V_DATE from dual;