#!/usr/bin/perl

use strict;
use Date::Manip;

my $limit = DateCalc( 'now', '- 45 days' );

while (<DATA>) {
    my $datestr = (split / : /)[0];  # note spaces around ":"
    print if ( ParseDate( $datestr ) > $limit );
}

__DATA__
Fri Dec  3 23:07:21 EST 2004 : Depth is : 234
Sat Dec  4 00:07:29 EST 2004 : Depth is : 123
Sat Feb 26 14:13:12 EST 2005 : Depth is : 4567