WordPress by default keeps an unlimited number of revisions for pages and posts (and custom post types – if enabled). If you want to limit the number of revisions, you can add this line of code to your wp-config.php:
define( 'WP_POST_REVISIONS', 5 ); // limits revisions to 5
If you want to completely disable revisions, you can add this line to your wp-config.php:
define('WP_POST_REVISIONS', false );