Even for a DTE field, you can specify edit codes (/ or -) that will allow entry and display of dates using 4 digit year.
This will result in 25-02-2085 being stored as 1850225 and 25-02-2101 being stored as 2010225.
You will need to change any screens that have dates of course, but the underlying database does not have to be changed.
Please note I haven't tested all the date functions with future dates, and some confirmation or advice from CA would be welcome.