How to get entity id by SKU and ATTRIBUTE ID in magento 2

I don't understand why are you fetching a product id by filtering with SKU and is_old attribute. Because SKU is already an unique value.

I am posting my answer here with two different cases.

Case 1: Get product Id using sku.

<?php 

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$productId = $objectManager->get('Magento\Catalog\Model\Product')->getIdBySku('your_sku');
print_r($productId);

?>

Case 2: Get old products using sku.

<?php 

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$products = $objectManager->get('Magento\Catalog\Model\Product')
            ->getCollection()
            ->addAttributeToFilter('is_old',1)
            ->addAttributeToFilter('sku',array('sku1','sku2',.....));

echo "<pre>";
print_r($products->getData());

?>

Instead of calling direct query, my suggestion is to get Magento collection by using product collection factory class:

Magento\Catalog\Model\ResourceModel\Product\CollectionFactory

Then filter that collection via addAttributeTofilter

<?php
namespace [YourClassNameSpace];
class [ClasssName]
{
     protected $_productCollectionFactory;

    public function __construct(
        ....
        \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory $productCollectionFactory,
        ...
    ) {
        $this->_productCollectionFactory = $productCollectionFactory;
        .....
    }

      public function  getProductCollection(){

         $collection = $this->_productCollectionFactory->create();
         // Assume tghat yes/no attribute code
         $collection->addAttributeToFilter('Is Old_ATTRIBUTE_CODE',1); //Use 1 for yes value
         /* Filter collection by multiple sk */
          $collection->addAttributeToFilter('sku',array('Sku1','sku2'.....,'sku2'));

      }

}