The system parameter called "Century Break" determines how the system interprets a 2-digit year. The default setting is 0, which causes all year values in 'yy' format to be converted to '19yy'. If Century Break is set to 50, then years less than 50 are converted to '20yy'. Set Century Break to 100 if you want a 2-digit year always to be interpreted as '20yy'.
For more information, see the Utilities reference manual, volume 1, chapter 11 (DBS Control).
If your system administrator doesn't agree that the Century Break parameter for your system should be changed, another possible solution is to manipulate the input string. Here is a demonstration:
select cast('20'||'06-07-25' as date) (format 'yyyy-mm-dd') as mydate;
*** Query completed. One row found. One column returned. *** Total elapsed time was 1 second.