I have coughs that just won't go away. is it an early sign of lung cancer? i have never smoked and i am 21 years old

Cough: There are a lot of things that can give you persistent cough. Although, cough is a very common symptom of lung cancer-however, it is less likely/ unlikely to be the case here- based on your age. More likely causes will include asthma, acid reflux/ post nasal drip due to sinus problem/deviated septum, infection/inflammation etc. Go to see your md and have yourself checked.

Probably not: Lung cancer in non smokers your age is extremely rare. If the cough persists you should be evaluated by your primary care doctor and/or a pulmonary physician. There are many causes of persistent cough the vast majority of them are benign. If you cough up any blood you should certainly be evaluated by a pulmonary physician.