Metalenses have emerged as a versatile platform for wavefront engineering, enabling compact and planar optical systems with unprecedented functional density. However, most reported metalenses rely on single-layer architectures that inherently support only a fixed focal length, which limits their application in tunable imaging and adaptive photonic systems. Dual-layer Moiré-type metalenses provide an alternative route toward zoom functionality by tuning the effective phase profile through relative rotation rather than axial translation. Despite this advantage, existing designs predominantly employ a paraxial parabolic phase approximation derived from the truncated expansion of the ideal lens phase. Such approximations become inaccurate under large-numerical-aperture (NA) conditions, where neglected higher-order phase components introduce spherical aberration accumulation and degraded focusing performance. Here, we present a non-paraxial design strategy for a dual-layer rotational zoom metalens based on the full ideal aberration-free phase function. By directly adopting the exact lens phase expression instead of the conventional parabolic approximation, higher-order phase contributions critical to large-NA operation are preserved. Zooming is achieved by engineering complementary phase distributions on two metasurface layers and dynamically modulating their combined phase via controlled rotation. To realize the target phase profiles, a dielectric metasurface operating at 10 GHz is designed using ceramic cylindrical resonators arranged in a triangular lattice. A systematic parametric optimization of lattice period, cylinder diameter, and height ensures complete a 2π phase coverage while maintaining transmission above 85%. The resulting phase-geometry mapping establishes a reliable unit-cell library for device construction. Based on this library, the dual-layer metalens is designed and evaluated through finite-difference time-domain simulations. A prototype with a 300 mm aperture is fabricated and experimentally characterized using three-dimensional near-field scanning measurements. Both simulations and experiments confirm continuous focal-length tuning as the rotation angle varies from -60° to 60°, corresponding to a focal-length range of 100 to 300 mm and a zoom ratio of 3:1. The device maintains a maximum NA of 0.83, and the measured focal spots remain well-confined and nearly diffraction-limited. The experimentally extracted focal-length variation agrees closely with theoretical predictions and simulations. These results verify the correctness of the non-paraxial design model and demonstrate the feasibility of achieving large-NA zooming in a dual-layer metasurface. This work provides a new pathway for lightweight variable-focus optics and holds significant potential for next-generation tunable imaging systems and compact optical platforms.