Vision and hearing tend to deteriorate with age, but smell usually holds up well. Losing it can be the first sign of something serious. Alzheimer's and Parkinson's can start with the loss of sense of smell. It can also be caused by a head or nose injury that damages the olfactory nerves. Slow-growing brain tumours can press on the olfactory nerves, preventing them working. But a far more common cause is allergy, leading to the lining of your nose becoming swollen and inflamed. There are treatments for allergic nasal problems that can restore your smell to normal. First, get a proper diagnosis, via referral to an ENT or allergy specialist. Allergies to simple things, like dust, feathers and household pets, can cause this kind of problem.
You could be lactose intolerant. Lactose is the natural sugar that is present in milk products. People who are lactose intolerant cannot digest it because they are lacking an enzyme called lactase, which breaks lactose down into glucose and galactose. Undigested lactose ferments in the stomach, causing a build-up of gas. Even if you were not lactose intolerant when you were younger, you may develop it, as it becomes more common with age. If you don't want to take a test to see if you are lactose intolerant, you could try to reduce or eliminate lactose from your diet and see if you are any better.