"We get them while they're young" should probably be printed on the front of every pack of cigarettes. According to the Centers for Disease Control and Prevention, nine out of 10 smokers try their first cigarette by 18, and 99% have tried it by age 26.
While cigarette use is on the decline in the United States, that still leaves decades of lifespan in which you can slowly murder yourself. Plenty of lifelong smokers, including my (very, very deceased) grandmother, have wondered, "I've smoked for [x] years, isn't it too late to quit now?"
Today we have an answer, and the answer is probably: no.
The same day the CEO of the world's largest tobacco company, Philip Morris, announced it would start to phase out cigarettes in favor of e-cigs, a new study has dropped concluding that it's never too late to quit, even in your 60s. Those who quit late in life still were less likely to die than their "Eh, I've made it this far!" peers.