How many shipments with weight of no more than 1,000 pounds were shipped by the oldest truck?
weight of no more than 1000 pounds refers to weight < 1000; oldest truck refers to Min (model_year)
SELECT COUNT(*) FROM truck AS T1 INNER JOIN shipment AS T2 ON T1.truck_id = T2.truck_id WHERE T2.weight < 1000 ORDER BY T1.model_year ASC LIMIT 1