<p>Fiber-reinforced polymer (FRP) composites are widely used in marine and offshore structures, yet long-term exposure to seawater degrades their mechanical response and alters failure mechanisms. While these effects are well documented experimentally, they are less frequently propagated into finite element (FE) material models used for structural prediction. This study examines how artificial seawater aging modifies the parameter set of LS-DYNA’s MAT54 (Enhanced Composite Damage) model. Mechanical data (tension, compression, and in-plane shear) were compiled for four laminate systems (glass/epoxy, glass/vinyl ester, glass/polyester, and carbon/epoxy) in both unaged and aged states. Stiffness, strength, and damage/softening parameters were investigated using calibration against the measured stress–strain behavior. Aging was represented through targeted updates to MAT54 inputs rather than ad hoc knock-down factors, enabling the model to capture coupled reductions in stiffness and strength across loading modes. The outcome is a set of aging-aware MAT54 parameter tables for each composite system that provide consistent fits to experimental behavior and a practical basis for FE simulation of environmentally exposed laminates. The analysis also indicates which (matrix-dominated) parameters are most sensitive to seawater exposure, offering guidance for selecting aging-dependent inputs. The calibrated datasets and workflow support more reliable prediction of structural performance and damage progression in FRP composites subjected to marine environments.</p>