Is it possible to have lung cancer at 21?!

defiantly a possiblity, but not a very likly one. Because he smokes, he does have a higher risk for lung cancer. But it could be other things.
"Pleurisy, in particular, is characterized by chest pain that appears each time a person inhales, and nearly disappears with exhalation. A severe coughing spell or two can sprain the chest muscles, and leave them aching for several days."
Good Luck!

http://heartdisease.about.com/cs/coronar…

In theory it's possible, but statistically extremely unlikely.

The other thing is that lung cancer doesn't actually cause any pain, at least not until the end stages. The sufferer usually notices these symptoms first: persistant cough, weight loss, extreme fatigue, night sweats. By the time you get these symptoms it's usually too late.

it's unlikely but it could happen. You should tell him to stop smoking so he doesn't have to worry about it.

yea it is totally possible especially smoking for that long of time span

Yes.

yes