find if date is older than 30 days

strtotime('2011-08-19 17:14:40') + 30 * 24 * 60 * 60 < time();

You can use Carbon as follows

if (30 - ((new \Carbon\Carbon($given_date, 'UTC'))->diffInDays()) < 0) {
    echo "The date is older than 30 days";
}

Try using something like this:

 if(strtotime('2011-08-19 17:14:40') < strtotime('-30 days')) {
     // this is true
 }

Besides, this string looks like it is stored in SQL as datetime/timestamp field. You can directly select all entries from your database with old dates using:

SELECT ... WHERE `datetime` + INTERVAL 30 DAY < NOW()

If you are on PHP 5.3 or higher you can do:

$someDate = new \DateTime('2011-08-19 17:14:40');
$now = new \DateTime();

if($someDate->diff($now)->days > 30) {
   echo 'The date was more than 30 days ago.';
}