Male 21. non smoker active lifestyle. i seem to be getting frequent colds with little cough about every other month. how likely is lung cancer?

Essentially zero: Although there is some data suggesting that lung cancer occurs at a bit younger age in never-smokers compared with smokers, in the absence of (for instance) immune system deficiency or underlying lung disease or the presence of cancer elsewhere in the body which could spread to the lungs, the likelihood of lung cancer at age 21 in an otherwise healthy non-smoker is virtually zero.