If you have **Order object** then you can get ***Guest Customer dob*** from `getCustomerDob()`.

In *,magento database*  you can get guest customer dob from `sales_flat_order` table's `customer_dob` column.

Suppose,you have order then you can get guest customer dob from

    $OrderObject=Mage::getMode('sales/order')->load('Order_Id');
    $DOb=$OrderObject->getCustomerDob(); // yyyy-mm-dd hh:mm:ss