Drupal code to restrict access to event nodes that are old and no longer valid.

custom_events.module

<?php
/**
 * @file
 * Code for the Custom Events module.
 */

/**
 * Implements hook_preprocess_node().
 *
 * Restrict access to events that more than a year old.
 */
function custom_events_preprocess_node(&$variables) {
  if ($variables['type'] == 'event') {
    $redirect = TRUE;
    // Do not redirect for certain user roles.
    if (!empty($variables['user'])) {
      $user_roles = $variables['user']->roles;
      if (in_array('Super admin', $user_roles) ||
        in_array('Administrator', $user_roles) ||
        in_array('Content admin', $user_roles) ||
        in_array('Event manager', $user_roles)
      ) {
        $redirect = FALSE;
      }
    }
    // Get the end date to use for comparison.
    $event_date = new DateTime($variables['field_event_date'][0]['value2']);
    // Get the current date.
    $date_to_check = new DateTime("now");
    // Calculate one year back from current date.
    $date_to_check->sub(new DateInterval('P1Y'));

    // Redirect to the front page if the one year has passed since the event
    // occured and if this is not a admin user viewing the event. This sets a
    // 302 HTTP status response code in the HTTP header.
    if ($event_date < $date_to_check && $redirect) {
      drupal_goto('<front>');
    }
  }
}