how to subtract
sysdate-'09-FEB-80'
SYSDATE-HIRE_DATE works just fine
but sysdate-an actual date gives
invalid identifier error

SQL> select sysdate-'09-feb-90'
2 from dual;
select sysdate-'09-feb-90'
*
ERROR at line 1:
ORA-01722: invalid number

This too gives error
1 select sysdate-to_date('09-02-80',DD-MON-YY)
2 from dual;

ERROR at line 1:
ORA-00904: "YY": invalid identifier

New to SQL.Thanks for the help