Background: Ketamine is an emerging treatment for treatment-resistant depression (TRD) associated with rapid and robust improvements in depressive symptoms and suicidality. However, the efficacy and safety of ketamine in transitional age youth (TAY; age 18–25) populations remains understudied. Methods: In this retrospective analysis, TAY patients ( n = 52) receiving ketamine for TRD were matched for sex, primary diagnosis, baseline depression severity, and treatment resistance with a general adult (GA) sample (age 30–60). Patients received four ketamine infusions over 2 weeks (0.5–0.75 mg/kg over 40 min). The primary outcome was the change in Quick Inventory of Depressive Symptomatology Self-Report 16-item (QIDS-SR16) over time. Secondary outcomes were changes in QIDS-SR16 suicidal ideation (SI) item, anxiety (Generalized Anxiety Disorder 7-item (GAD-7)), and adverse effects (ClinicalTrials.gov: NCT04209296). Results: A significant main effect of infusions on reduction of total QIDS-SR16 ( p < 0.001), QIDS-SR16 SI ( p < 0.001), and GAD-7 ( p < 0.001) scores was observed in the TAY group with moderate effect sizes, indicative of clinically significant improvements in depression, anxiety, and suicidality. There were no significant differences between TAY and GA groups on these measures over time, suggesting comparable improvements in both groups. Safety and tolerability outcomes were comparable between groups with only mild, transient adverse effects observed. Conclusion: Ketamine was associated with comparable clinical benefits, safety, and tolerability in a TAY sample as compared to a matched GA TRD sample.