エラーメッセージ：FatalThrowableError in DateTimeType.php line 53:
Call to a member function format() on string

ソース：
public function AA($pointRate, $product, $customerKbn = null, $lastPointProductVipDateStart)
{
try {
$em = $this->getEntityManager();

$pointRateEntity = new PointProductRate();
$pointRateEntity->setPlgPointProductRate($pointRate);
$pointRateEntity->setProduct($product);
$pointRateEntity->setProductId($product->getId());

$date = $lastPointProductVipDateStart;

$now = date($date);

$pointRateEntity->setPointDateStart($now);
echo $pointRateEntity['point_date_start'];

$em->persist($pointRateEntity);

if(!is_null($customerKbn)){
$pointCategory = new PointCategory();
$pointCategory->setPlgPointProductRateId($pointRateEntity->getPlgPointProductRateId());
$pointCategory->setCustomerKbn($customerKbn);
$pointCategory->setDelFlg(Constant::DISABLED);
$em->persist($pointCategory);
}

$em->persist($product);

// DB更新
$em->flush();
} catch (NoResultException $e) {
throw new NoResultException();
}
}