Gamma radiation shielding properties of Acacia mangium wood (ages 3 – 15 years) were investigated at 662 keV (¹³⁷Cs). Mass attenuation coefficients, linear attenuation (µ), and half-thickness were measured; the attenuation properties were discussed include linear attenuation (µ) and mass attenuation (µ/ρ). Additionally, the paper will explore the feasibility of substituting traditional shielding materials, such as concrete and copper, with these tropical wood species for low-energy gamma-ray diagnostic applications. Two mathematical models have been developed to predict wood density based on variations in relaxation length and half-thickness values. The results indicate that the three-year-old Acacia mangium tree has the longest relaxation length at 83.33 cm and the lowest density at 0.43 g/cm³. In contrast, the 15-year-old tree has the shortest relaxation length of 28.56 cm and the highest density at 0.76 g/cm³. Furthermore, the results show that the 3-year-old Acacia mangium tree’s wood has the maximum half-thickness value (57.75 cm), while the fifteen-year-old tree’s wood has the lowest half-thickness value (about 19.85 cm). A good agreement (greater than 85% in most cases) was observed between the measured values and predicted ones. A strong linear correlation was observed between the measured density and the age of the tree (R² = 0.824), as well as between the estimated density and the age of Acacia mangium trees (R² = 0.952). Acacia mangium shows potential as a sustainable gamma shielding material for low-energy applications.