I am just curious about what are the first symptoms of lung cancer, how long does it take a smoker to get it and what is the average age of diagnosis?

None: Early stage lung cancers do not have any symptoms there is no accepted mass screening test for eararly detection low yield do not justify mass screening with spiral ct scans , smoking is a convincing cause, some lucky ones may escape, but you can't predict who will get and who will not get , and how long you need to smoke to get lung cancer.

Often asymptomatic.: This is often asymptomatic with about 5-15% detected from symptoms. Pesistent cough is the usual presenting sign, with hemoptysis, wheeze, dyspnea or difficulty breathing, depending on its site. Hoarseness, and respiratory failure can mean spread beyond the lungs. This occurs most at 55-65 years and since smoking is the most common cause, it likely takes from its start so don't start smoking.

Often none: Lung cancer is often asymptomatic, resulting in late stage diagnosis. The following links may assist you in each portion of your question: http://goo.Gl/2yuxg and http://goo.Gl/vvhhy and http://goo.Gl/gu9ms.