Old files not being deleted

This issue has to do with not deleting files if it's over 30 days old. I follow D7 Core
drupal_delete_file_if_stale() D7 is called by these 2 functions: drupal_clear_css_cache() D7 & drupal_clear_js_cache() D7

If you wish to adjust this, there are 3 setting in advagg that have to do with time.

/**
 * Default stale file threshold is 30 days for mtime.
 */
define('ADVAGG_STALE_FILE_THRESHOLD', 2592000);
variable_get('advagg_stale_file_threshold', ADVAGG_STALE_FILE_THRESHOLD);
// Compares against filemtime()

/**
 * Default stale file threshold is 15 days for atime.
 */
define('ADVAGG_STALE_FILE_LAST_USED_THRESHOLD', 1296000);
variable_get('advagg_stale_file_last_used_threshold', ADVAGG_STALE_FILE_LAST_USED_THRESHOLD);
// Compares against fileatime()

/**
 * Default file last used check-in is 12 hours.
 */
define('ADVAGG_FILE_LAST_USED_INTERVAL', 1296000);
variable_get('advagg_file_last_used_interval', ADVAGG_FILE_LAST_USED_INTERVAL);
// How often the cache_advagg cache is updated.

When adjusting these settings make sure that:
advagg_file_last_used_interval is longer then your cron runs.
advagg_stale_file_threshold is at least 4x advagg_file_last_used_interval
advagg_stale_file_last_used_threshold is 1/2 of advagg_file_last_used_interval

going to move the defaults to 6 and 3 days. Marking this as fixed; let me know if you have any other issues. This might be related to your issue as well #1161570: Flushing the advagg cache not working.