Human Papillomavirus (HPV) vaccine has been shown to prevent cervical cancer. Numerous studies have examined factors associated with HPV vaccine series initiation, but little is known about factors associated with age of initiation of HPV vaccine. Using cross-sectional data from the 2011 National Immunization Survey-Teen, this study examined the relationship between Advisory Committee on Immunization Practices' recommended age at initiation of the HPV vaccine series and socioeconomic status, race/ethnicity, and health insurance among 13-17 year-old females who received at least one HPV vaccine shot (n=5,965). On-time initiation of HPV vaccine series was significantly associated with having public health insurance (AOR: 1.825, 95% CI: 1.266, 2.631). Females with college-graduated mothers (AOR: 0.669, 95% CI: 0.487, 0.918) or household income greater than $75,000 (AOR: 0.746, 95% CI: 0.568, 0.98) were less likely to initiate on-time. Research is needed to further investigate the reasons for late initiation among these subgroups.