use strict;
use warnings;

my $cutoff = 600;
my $c = 0;

while (<DATA>) {
    $c++ if (split /\t/)[0] > $cutoff;
}

print "$c over $cutoff\n";

__DATA__
10    alpha
30    bravo
60    charlie
100    delta
500    echo
600    foxtrot
4    golf
22    hotel
900    igloo
800    juliet
999    kilo
[download]

Or alternatively:

$c++ if m/^(\d+)/ && $1 > $cutoff;