mysql> set @t='2007-01-01 00:00:00';
Query OK, 0 rows affected (0.00 sec)

mysql> select addtime('0000-00-00 00:00:00',timediff(now(),@t));
+---------------------------------------------------+
| addtime('0000-00-00 00:00:00',timediff(now(),@t)) |
+---------------------------------------------------+
| 0001-03-16 19:31:07                               |
+---------------------------------------------------+
1 row in set (0.00 sec)