Background/Objectives: Frailty is a multidimensional geriatric syndrome associated with increased vulnerability to adverse health outcomes. In India, where linguistic and cultural diversity is vast, there is a need for culturally adapted frailty assessment tools. This study aimed to translate, culturally adapt, and evaluate the reliability and validity of the Bengali version of the FAST among community-dwelling older adults in Kolkata, India. Methods: A community based cross sectional study was conducted among 217 older adults (≥60 years) residing in wards 57 and 58 of the Kolkata Municipal Corporation. Participants were selected through systematic random sampling. The English version of the FAST was translated and back-translated following standard guidelines. Reliability was assessed using Cronbach’s alpha, intra-class correlation coefficients and Cohen’s kappa. Construct validity was tested using confirmatory factor analysis, and criterion validity was evaluated against the Fried Frailty Phenotype using Receiver Operating Characteristic analysis. Results: The Bengali FAST demonstrated good internal consistency (Cronbach’s α = 0.806), strong intra-rater (ICC = 0.85) and inter-rater reliability (ICC = 0.81), and substantial inter-rater agreement (κ = 0.602, p < 0.001). CFA supported the factorial validity of the scale (CFI = 0.966, TLI = 0.960). Criterion validity analysis showed high sensitivity (0.810) and good discriminative ability (AUC = 0.843, p = 0.002). Conclusions: The Bengali version of the FAST is a reliable, valid, and culturally appropriate instrument for assessing frailty among Bengali-speaking older adults. Its integration into routine geriatric care can facilitate early detection and preventive interventions, thereby improve overall health and promote healthy ageing.