The present work aims to assess the age hardening of microalloyed Mg–Zn–Mn alloy reinforced with Ca10(PO4)6(OH)2 (hydroxyapatite, HAp) particles to impart mechanical strength without deteriorating their degradation and biocompatibility behavior for their suitability toward resorbable fixation devices. The hydroxyapatite powder was synthesized with high purity. Mg–Zn–Mn (ZM31) and Mg–Zn–Mn/HAp (ZM31/HAp) were stir-cast, homogenized, and solution-treated to achieve uniform dissolution. Further, they were given a range of aging treatments (175 °C for 0, 5, 10, 25, 50, and 100 h), and the age hardening was measured as Vickers microhardness. The solution-treated and peak-aged (175 °C × 50 h) samples were further investigated using optical and electron microscopy, tensile testing, electrochemical corrosion testing, dynamic mechanical analysis, and biocompatibility. The peak-aged ZM31 sample revealed the highest ultimate strength (134.09 ± 5.46 MPa). The aging treatment resulted in notable improvement in ductility in ZM31 (8.72 ± 1.38%) and yield strength in ZM31/HAp (82.50 ± 1.43 MPa). The rapid strain-hardening behavior was distinctly visible in peak-aged samples in the initial stage of deformation. The amplitude-dependent internal friction confirmed the active solute and age-hardening mechanisms in agreement with the Granato–Lücke model. All samples displayed favorable cell viability (>80%) and cell adhesion behavior; however, their hemocompatibility and biodegradation need further consideration.