update year in date field

please help me on this.. I wanted to update year in the date field which is currently in this format "DD-MON-YY". But actually the year suppose to be "1986" turn out to be "2086"
How can I change the year from "20" to "19"

I've tried run this SQL but it change all the date and month

update CUSTOMERS set DATE_OF_BIRTH=DATE_OF_BIRTH - 100 * 365;

it just didn't work the way I want it to..

PLEASE HELP!!

In Oracle 9i you can do:

select sysdate - to_yminterval('100-00') from dual;

Regards,
Dan