public static function age($start, $end = null) {
		if (empty($start) && empty($end) || $start == $end) {
			return 0;
		}

		if (is_int($start)) {
			$start = date(FORMAT_DB_DATE, $start);
		}
		if (is_int($end)) {
			$end = date(FORMAT_DB_DATE, $end);
		}

		$startDate = $start;
		if (!is_object($start)) {
			$startDate = new CakeTime($start);
		}

		$endDate = $end;
		if (!is_object($end)) {
			$endDate = new CakeTime($end);
		}

		if ($startDate > $endDate) {
			return -1;
		}
		$oDateInterval = $endDate->diff($startDate);
		return $oDateInterval->y;
	}