Find birthday from NIC number (Sri Lanka) PL/SQL code

This program is design to find birthday from NIC number (Sri Lanka). Fell free to comment and optimize the code.

DECLARE
    TYPE daysInMonthArray IS VARRAY(12) OF VARCHAR2(2);
    days daysInMonthArray;
    year1 VARCHAR2(4);
    idText VARCHAR2(12);
    dayOfMonth NUMBER;
    j NUMBER;
    dateOfBirth DATE;
    daysOfYear NUMBER;
    month1 VARCHAR2(4);
BEGIN
    daysOfYear := 0;
    idText := '900780826v'; -- Enter your NIC number here
    days := daysInMonthArray('31','29','31','30','31','30','31','31','30','31','30','31');
    year1 := '19' || SUBSTR(idText,0, 2);
    daysOfYear := SUBSTR(idText,3, 3);
    IF (daysOfYear > 500) THEN
        daysOfYear := daysOfYear-500;
    END IF;