To disable comments on posts older than date X in WordPress you can use the snippet below.
Sample mySQL
UPDATE wp_posts SET comment_status = 'closed' WHERE post_date < '2013-01-01' AND post_status = 'publish'
To disable comments on posts older than date X in WordPress you can use the snippet below.
UPDATE wp_posts SET comment_status = 'closed' WHERE post_date < '2013-01-01' AND post_status = 'publish'