There are many many reasons for hairloss from within the body and outside the body. It is extremely unlikely related to old age. What were the urine and blood test results? Also, I would recommend avoiding aspirin, as it can cause damage to the stomach lining and is really not very effective. We have much safer more effective medications that can be used based on the blood results. Please speak with your veterinarian about these options as well as the urine/blood results. How much does your little guy weigh? How many cups or ounces of water does he drink? What is his appetite like? Until a culprit can be found, taking him out in the sun with a light doggy jacket/sweater may be beneficial.
Thank you for your answer. I am taking him to his vet at the end of the month.