PHP check if date is 30 days in the past

I'm having a bit of a problem here.

I insert a date into the database: date_last_applied.

I can just call this by using $row['date_last_applied'], of course. Now, I need to check if this inserted date was 30 days ago and if so, execute an action.

$query = "SELECT date_last_applied FROM applicants WHERE memberID='$id'";
$result = mysql_query($query);

while($row = mysql_fetch_array($result)) {
    $date = strtotime($row['date_last_applied']);

}

That's about all I have.. I tried some things, but they all failed. :(