Context: There is a lack of research that prospectively estimates the age of initiation of electronic cigarette use in U.S. youth. Younger ages of initiation of tobacco product use are associated with greater exposure to nicotine, and recently e-cigarette use has been associated with subsequent cigarette initiation. This study sought to estimate the distribution of the age of first reporting of e-cigarette use outcomes among youth never e-cigarette users overall, by sex and by race/ethnicity, prospectively. Methods: Secondary analysis of the Population Assessment of Tobacco and Health (PATH) youth dataset (ages 12-17) across waves 1 (2013-2014), 2 (2014-2015), 3 (2015-2016), and 4 (2016-2017) were conducted. Four outcomes are presented, age of first report of: (i) susceptibility to use, (ii) ever, (iii) past 30-day use, and (iv) “fairly regular” e-cigarette use. Each outcome was prospectively estimated using participant age when they entered the study and the number of weeks between the last report of never use and the first report of each outcome across waves. Weighted survival analyses for interval censoring accounting for the complex survey design were implemented. Results: Among youth non-susceptible to e-cigarettes, 50.2% became susceptible to e-cigarette use by age 18. There were no statistically significant differences in the age of first report of susceptibility to e-cigarette use by sex or by race/ethnicity in this nationally representative sample of U.S. youth. Among never users, 41.7%, 23.5% and 10.3% initiated ever, past 30-day and “fairly regular” e-cigarette use by the age of 18, respectively. Less than 10% initiated ever e-cigarette use between the ages of 18 and 21. Boys had a higher risk of first reporting ever, past 30-day and “fairly regular” e-cigarette use at earlier ages than girls. Non-Hispanic Blacks and Other racial/ ethnic groups were less likely than Non-Hispanic Whites to initiate ever e-cigarette use at earlier ages, and there was no difference between Non-Hispanic Whites and Hispanics. Hispanic, Non-Hispanic Black and Other racial/ethnic youth were less likely to first report past 30-day use and “fairly regular” e-cigarette use at earlier ages than Non-Hispanic White youth. Conclusion: This paper provides information on specific ages of the first report of e-cigarette use behaviors by sex and by race/ethnicity that can be used to tailor culturally e-cigarette interventions on specific windows of opportunity before youth begin using e-cigarettes or escalating their use.