Two problems:

first, how systems store this information (when the password has been changed recently) is diffferent from one system to the next. derekludwig has told you how some Linux variants do it, but in other UNIXes (or UNIX-like) systems this is done differently. In AIX, for instance, it is done in the /etc/security-directory in several files. To really help you here you wll have to post more details about your system.

second: as a non-root user you simply cannot get this information. It is none of your business (from a systems POV). Everything else would be a severe security-breach.

I hope this helps.

bakunin