Data came from the 2014 2015 Tobacco Use Supplement to the Current Population Survey. We found that onset of regular smoking at age 18 to 20 years was associated with higher odds of nicotine dependence and lower odds of attempting and intending to quit. These outcomes were observed with regular smoking initiation at age 18 to 20 as well as before age 18, suggesting that efforts to prevent access to tobacco products before age 21 could reduce nicotine addiction and promote cessation later in life....