My machine is in Japan.

modena@makoto 07:17:50/100804(/export/pkgsrc)% ls -l /etc/localtime 
lrwxr-xr-x  1 root  wheel  25 Apr  6 12:51 /etc/localtime -> /usr/share/zoneinfo/Japan

modena@makoto 07:17:27/100804(~)% date -j -d '1970/01/01 08:59' '+%s'
date: Cannot parse `1970/01/01 08:59'
modena@makoto 07:17:30/100804(~)% date -j -d '1970/01/01 09:00' '+%s'
0

This (argument to the 'date command') can not be used to get serial date of the birthday before 1970/01/01. Even 64 bit date ?

SQL seems to have datediff function.

mysql> SELECT DATEDIFF( STR_TO_DATE('08-04-2010','%d-%m-%Y'),
	                STR_TO_DATE('10-12-1960','%d-%m-%Y'));
+-----------------------------------------------------------+
| DATEDIFF( STR_TO_DATE('08-04-2010','%d-%m-%Y'), 
            STR_TO_DATE('10-12-1960','%d-%m-%Y'))           |
+-----------------------------------------------------------+
|                                                     18016 |
+-----------------------------------------------------------+
1 row in set (0.00 sec)

It is dd-mm-yyyy, European Style for here. Converting a date string which is before 1970 into a timestamp in MySQL.