Highlight old post on wordpress -

how highlight old post on wordpress, have site has thumbnails of videos. want have older videos gray out or have div style opacity main focus of viewer new post. possible?

test posts many days old date (in case 46 days)

<?php $mylimit=46 * 86400; //days * seconds per day //$post_age = date('u') - get_post_time('u'); $post_age = date('u') - mysql2date('u', $post->post_date_gmt); if ($post_age < $mylimit) { echo 'this post within date limit '; } ?> 

also can use plugins old post notifier or old posts highlighter.