I have used this trigger to restrict the insertion of those records for which the date of birth is less then 18. This is working fine for the new insertion, but I also want to restrict the modification of the date of birth if it is set to less then 18. Please tell how can I do this?

```
DELIMITER $$
CREATE TRIGGER `test_candidate_before_insert` BEFORE INSERT ON `candidate` FOR EACH ROW
BEGIN
    IF 
        DATEDIFF(CURDATE(), NEW.date_of_birth)/365 < 18     
    THEN
        SIGNAL SQLSTATE '12345';
    END IF;
END$$   
DELIMITER ;

```