If your dates are in Epoch seconds and fall in the range Fri Dec 13 20:45:52 1901toTue Jan 19 03:14:07 2038 (inclusive), subtract one from the other and convert the seconds to days:

$seconds = $recent - $earlier;

If you have distinct DMYMHS values or are worried about the range limitations of Epoch seconds, use the Date::Calc module from CPAN. It can calculate the difference between dates:

use Date::Calc qw(Delta_Days);
$days = Delta_Days( $year1, $month1, $day1, $year2, $month2, $day2);

It also calculates the difference between a pair of dates and times:

use Date::Calc qw(Delta_DHMS);
($days, $hours, $minutes, $seconds) =
  Delta_DHMS( $year1, $month1, $day1, $hour1, $minute1, $seconds1,  # earlier
              $year2, $month2, $day2, $hour2, $minute2, $seconds2); # later

One problem with Epoch seconds is how to convert the large integers back to forms that people can read. The following example shows one way of converting an Epoch seconds value back to its component numbers of weeks, days, hours, minutes, and seconds:

$bree = 361535725;          # 16 Jun 1981, 4:35:25
$nat  =  96201950;          # 18 Jan 1973, 3:45:50

$difference = $bree - $nat;
print "There were $difference seconds between Nat and Bree\n";
There were 265333775 seconds between Nat and Bree

$seconds    =  $difference % 60;
$difference = ($difference - $seconds) / 60;
$minutes    =  $difference % 60;
$difference = ($difference - $minutes) / 60;
$hours      =  $difference % 24;
$difference = ($difference - $hours)   / 24;
$days       =  $difference % 7;
$weeks      = ($difference - $days)    /  7;

print "($weeks weeks, $days days, $hours:$minutes:$seconds)\n";
(438 weeks, 4 days, 23:49:35)

use Date::Calc qw(Delta_Days);
@bree = (1981, 6, 16);      # 16 Jun 1981
@nat  = (1973, 1, 18);      # 18 Jan 1973
$difference = Delta_Days(@nat, @bree);
print "There were $difference days between Nat and Bree\n";
There were 3071 days between Nat and Bree

use Date::Calc qw(Delta_DHMS);
@bree = (1981, 6, 16, 4, 35, 25);   # 16 Jun 1981, 4:35:25
@nat  = (1973, 1, 18, 3, 45, 50);   # 18 Jan 1973, 3:45:50
@diff = Delta_DHMS(@nat, @bree);
print "Bree came $diff[0] days, $diff[1]:$diff[2]:$diff[3] after Nat\n";
Bree came 3071 days, 0:49:35 after Nat

The documentation for the CPAN module Date::Calc