Al-Mg-Zn is a crossover between the Al-Mg-(Mn) and Al-Zn-Mg-(Cu) alloys.  It exhibits an excellent balance of high strength, good formability, and superior corrosion resistance. The primary strengthening phases of this alloy are the T-phase and its precursors; however, its aging response rate is relatively slow. To address this issue, the present study systematically investigates the effects of Cu microalloying and pretreatment processes (including pre-aging, pre-deformation, and two-step aging) on the precipitation behavior, microstructure, and mechanical properties of Al-Mg-Zn alloys. The results demonstrate that combined pretreatments outperform conventional single pre-aging, achieving a concurrent enhancement of aging kinetics, strength, and ductility. Such enhancement is attributed to the synergistic effects of combined pretreatments: high-density T-phase precursors generated during pre-aging, and deformation-induced dislocations collectively accelerate the subsequent formation of hardening phases by providing heterogeneous nucleation sites and rapid diffusion pathways. Increased pre-deformation further enhances aging kinetics through dislocation-mediated nucleation and precipitate growth, thus yielding high-density T-type precipitates with narrowed precipitation-free zones (PFZs). Cu addition amplifies these benefits by promoting desirable precipitate growth while inhibiting their coarsening during final low-temperature aging. The optimized strategy (pre-aging at 100 °C, followed by 15% cold rolling and final aging at 120 °C) enables the Cu-containing alloy to achieve an exceptional strength-ductility synergy (a yield strength of 520 MPa with an elongation of 11%) and a rapid hardening rate (a peak aging time of only 32 h). This work proposes a strategic optimization scheme to mitigate the strength-ductility trade-off, providing a theoretical guideline for the design of high-performance aluminum alloys.