sub age {
    # Assuming $birth_month is 0..11
    my ($birth_day, $birth_month, $birth_year) = @_;

    my ($day, $month, $year) = (localtime)[3..5];
    $year += 1900;

    my $age = $year - $birth_year;
    $age-- unless sprintf("%02d%02d", $month, $day)
               >= sprintf("%02d%02d", $birth_month, $birth_day);
    return $age;
}