Purpose: Calculation of a biological heart age offers an alternative to absolute risk for characterizing cardiovascular risk by describing risk relative to an individual with normal health. We examined risk factors contributing to differences between biological and chronological heart age in young adults. Methods: The Coronary Artery Risk Development in Young Adults study included 2264 Black and White men and women who attended examination years 10 through 25. We estimated biological heart age using the nonlaboratory-based Framingham 10-year cardiovascular disease risk calculator. Trends in risk factors were examined cross-sectionally and longitudinally. Results: Biological heart ages for Black participants were 5.6 years older than their chronological ages over 15 years (P < .001). In longitudinal analyses, urinary albumin–creatinine ratio and alcohol intake were statistically significantly related to higher biological compared with chronological heart age, whereas physical activity and education were statistically significantly related to negative heart age differences (P < .001). Trends were similar in cross-sectional analyses at all time points. Conclusions: Most risk factors driving biological heart age, including race, education, physical activity, and urinary albumin–creatinine ratio, contributed to heart age differences cross-sectionally and longitudinally suggesting that risk factors related to adverse biological aging are important at younger and older ages.