My mum is having cough lately. Is it because due to old age? Any way to prevent her cough to become worst?

Chronic Cough. Cough which is chronic (long standing), could be due to many causes. Old age by itself should not cause cough. Smoking is one big cause and so is reflux disease., old age by itself should not cause cough. Infections some serious like tuberculosis could cause cough. There are some structural disorders like pulmonary fibrosis that are more serious. She needs to be check out and get an xray.
See. Reflux, asthma, and post nasal drip are your common causes. It is not age.