Where the numbers come from
Each choice moves the starting age up or down by an average effect seen in large studies: smoking throughout adult life shortens life by about 10 years on average, being regularly active adds roughly 3 years, severe obesity and heavy drinking each take several years off, and women live about 5 years longer than men on average. Real lives vary far more than any average. The good news in the research is that quitting smoking and moving more help at any age.