SQL> select to_date('31-DEC-4712') - sysdate          "Days left",
  2         months_between('31-DEC-4712', sysdate)    "Months left",
  3         months_between('31-DEC-4712', sysdate)/12 "Years left"
  4  from   dual;

 Days left Months left Years left
---------- ----------- ----------
989234.387  32501.1738 2708.43115

SQL*Plus: Release 9.2.0.1.0 - Developer's Release on Sun Jul 25 22:06:24 2004

SQL> SELECT TO_DATE('31-DEC-4712','DD-MON-YYYY') +1 FROM dual;

TO_DATE('31
-----------
01-JAN-4713

1 row selected.

SQL> SELECT DATE '9999-12-31' FROM dual;

DATE'9999-1
-----------
31-DEC-9999

1 row selected.

SQL> SELECT DATE '9999-12-31' +1 FROM dual
SELECT DATE '9999-12-31' +1 FROM dual
                         *
ERROR at line 1:
ORA-01841: (full) year must be between -4713 and +9999, and not be 0