This paper introduces and investigates the performance of a system where an unmanned aerial vehicle (UAV) is utilized to assist terrestrial backscattering devices (BDs) in wireless energy charging and data transmission. The UAV task is data collection through the backscatter communication with finite block length. To assess performance, the study not only considers energy efficiency (EE) but also derives closed-form expressions for age-of-information (AoI). The block error rate (BLER) expression is approximated using Gaussian-Chebyshev quadrature and the first-order Riemann integral. Furthermore, the optimization problem is solved to maximize EE and minimize transmit power through a search algorithm. Both EE and spectral efficiency (SE) are investigate via the number of transmission bits. The analytical and simulation results show that the optimized EE and minimum transmit power of UAV can be obtained by selecting an appropriate packet length and UAV altitude. Besides, the Rician factor K also has a significant impact on BLER of the considered system. Finally, the study points out that the system performance is strongly influenced by factors such as the utilized bandwidth, the specific operating environments, and the elevation angle of UAV.