At age 65, Supplemental Security Income (SSI) turns from a disability program into a retirement program—the disability eligibility requirements end, and applicants qualify on a financial basis alone. People who begin receiving SSI at age 65 or later are often considered in research separately from those under age 65 who enter through the disability pathway. Yet, these groups may not be that dissimilar. Applicants approved to receive SSI just after the disability eligibility requirements end may have been marginally eligible on a disability basis but were easily approved once the disability requirements were waived. This paper asks the overarching question: “Is age at first SSI receipt indicative of underlying differences in employment histories and population characteristics?” To answer this question, this study will use merged, longitudinal administrative microdata from Washington state to compare employment histories and population characteristics among people who first receive SSI in the three years before SSI’s disability requirements end (ages 62 64) and the three years after (ages 65-67). Differences between these groups could indicate that the age 65 threshold reflects underlying population differences; similarities, on the other hand, could indicate a mismatch between the age 65 threshold and underlying population needs. Findings from this study will contribute to longstanding policy debates about age based eligibility rules for social insurance programs.