well, at least in medicine the latent period for smoking is 15 ish years. if nothing happens by then, you can be considered more or less out of the window for cigarette damages to manifest further.  also lung cancer incidence did peak some years ago. and smoking prevalence has only been going down.   s-in-lung-disease/lung-cancer-trend s-brief/lung-cancer-prevalence-and- incidence
United States