#last modify time of /usr/bin:
print scalar localtime((stat("/usr/bin"))[9]);
# Thu May 14 13:52:17 2009

 my $SECONDS_IN_DAY = 60*60*24;
 $days_old =  (time-(stat($dirname))[9]) / $SECONDS_IN_DAY;
 if($days_old > 5){
   #do_something
 }