What kind of likelihood is there of a teenager getting lung cancer?

Rare. Lung cancer from smoking would be very rare in a teenager. There are many forms of lung cancer. Cancer can be in the lung due to spread of cancer from some other body area. If this is in relation to smoking, just don't. It will be the best thing you ever do for yourself not to smoke or if you do, to stop!
Tumor Board this AM. Reminded me that young men/boys with lung masses are much more likely to have testis cancer in their lungs than primary lung cancer (rare to unheard of). An HCG and Alpha feto-protein blood test and testicular exam and ultrasound are in order. Girls can get ovarian dysgerminomas, but less seen than testis cancer, associated with undescended testis too!