Show min and max taxonomy values

Not sure but try this:

  function get_years ($taxonomies, $args){
      $output = array();
      $hlterms = get_terms($taxonomies, $args);
      foreach($hlterms as $term){
           $term_taxonomy = $term->year;
           array_push($output, $term->name);
     } return $output;
  }

$taxonomies = array ('year');
$args = array ('hide_empty'=>true);
$year = get_years($taxonomies, $args);
echo min($year);