Ah! Thank you. That helped me figure it out. Here is my solution to show a dot if file is less than 6 months old:
$age = strtotime( get_sub_field('file_date'));
$now = strtotime("now");
<span class="age"><?php if ($now - $age < 15778800) { echo "<i class='fas fa-circle'></i>"; }?></span>