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 offer an alternative pathway to achieving zoom functionality by modulating the effective phase profile through relative rotation rather than axial translation. Despite this advantage, existing designs predominantly employ a paraxial parabolic phase approximation based on 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 accumulated spherical aberration and degraded focusing performance. Here, we present a non-paraxial design strategy based on the full ideal aberration-free phase function for a dual-layer rotational zoom metalens. By adopting the exact lens phase expression rather than the conventional parabolic approximation, this approach preserves the higher-order phase contributions critical to large-NA operation. 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 a complete 2π phase coverage while maintaining a transmission above 85%. The resulting phase-geometry mapping establishes a reliable unit-cell library for device implementation. Leveraging this library, the dual-layer metalens is designed and its performance evaluated through finite-difference time-domain (FDTD) 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 that continuous focal-length tuning is achieved 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 achieves a maximum NA of 0.83, and the measured focal spots remain nearly diffraction-limited. The experimentally extracted focal-length variation agrees closely with theoretical predictions and simulations. These results validate the non-paraxial design model and demonstrate the viability of large-NA zoom operation in a dual-layer metasurface. This work offers a promising route for lightweight variable-focus optics and holds significant potential for next-generation tunable imaging systems and compact optical platforms.