The Advisory Committee on Immunization Practices recommends routine human papillomavirus (HPV) vaccination at 11-12 years; the series can begin at age 9. U.S. HPV vaccination coverage is lower than other adolescent vaccinations. One proposed strategy to increase coverage is initiation at 9-10 years. We systematically reviewed studies addressing vaccination at age 9 to identify and evaluate evidence regarding potential programmatic advantages. Among 30 publications from 2014 to 2024 there were retrospective cohort studies ( = 11), intervention studies with a component focused on vaccination at 9-10 ( = 12), and studies of feasibility or acceptability by providers or caregivers ( = 7). While retrospective analyses found earlier initiation associated with completion, limitations in methodology preclude a cause-and-effect interpretation. Impact of age 9 vaccination is difficult to isolate in intervention studies that had multiple components. While initiating vaccination at age 9 is feasible, questions remain regarding the benefit of this approach to increase coverage.