Number of years in the past that custom date fields will display in drop down boxes.

• add in config_defaults_inc.php : back_year_count (ie forward_year_count)
  $g_past_year_count = 0 ;//defaut 0

• patch in core\date_api.php

$t_past_years = config_get( 'past_year_count' ) ;

and twice :
$t_start_year = $t_current - $t_past_years ;