Background/Objectives: Antimicrobial resistance (AMR) poses a disproportionate mortality risk to older adults, yet this demographic is often overlooked in stewardship interventions compared to the general population or other at-risk/vulnerable groups. While awareness campaigns exist, it remains unclear how knowledge gaps influence antibiotic usage behaviors among the elderly in lower middle-income settings like Vietnam. This study evaluates antibiotic literacy and usage patterns among older adults (aged ≥ 60 years) in Hanoi, identifies sociodemographic predictors of these domains, and determines whether knowledge deficits predict inappropriate practices. Methods: A descriptive cross-sectional study was conducted on 177 retired individuals aged 60-86 years (44% male, 56% female) in Gia Lam Commune, Hanoi, via face-to-face interviews. A structured questionnaire, adapted from World Health Organization and validated regional studies, assessed demographics, knowledge, AMR awareness, and practices. Multivariable linear regression identified independent predictors of these outcome scores. Results: Usage prevalence was high; 60% of participants reported taking antibiotics in the past year. Although 91% acknowledged the personal threat of "antibiotic resistance", profound functional misconceptions persisted: 58% failed to distinguish antibiotics from analgesics (paracetamol), and 67% incorrectly believed antibiotics are effective for treating fever. Of concern, 95.5% mistakenly thought that the human body develops resistance to the medication, and 55% perceived AMR as a foreign issue irrelevant to Vietnam. Regression analysis revealed that advanced age (≥ 78 years) was a strong negative predictor of knowledge (β = -2.0; p < 0.001), while higher knowledge scores were significantly associated with better adherence to safe practices (β = 0.15; p = 0.045). Conclusions: Older adults in Vietnam demonstrate high superficial awareness of AMR but harbor critical misconceptions, particularly conflating antibiotics with analgesics and falsely believing the human body develops resistance. Furthermore, advanced age emerged as a significant vulnerability factor for low health literacy. Since greater knowledge directly predicts safer usage practices, interventions must move beyond general warnings to correct specific mechanistic misunderstandings, thereby mitigating self-medication and resistance in this highly vulnerable population.