Mortality is especially reduced by quitting earlier in life.

Smokers who quit before the age of 50 experience better health and have half the risk of dying within the next 15 years compared with those who continue to smoke.

U.S. Department of Health and Human Services. The Health Benefits of Smoking Cessation: A report of the Surgeon General. Rockville, MD: US Department for Health and Human Services, 1990.

Doll R, Peto R, Boreham J, Sutherland I. Mortality in relation to smoking: 50 years’ observations on male British doctors. BMJ. 2004; 328: 1519.