We propose and report the implementation of a multiband and photonically amplified fifth-generation (5G) new radio (NR) system based on radio over fiber technology and four-wave mixing (FWM) nonlinear effect. A piece of highly nonlinear fiber has been employed to stimulate FWM, which enables photonics-assisted RF amplification up to millimeter waves. Experimental results demonstrate a uniform and stable 15 dB ultra-wideband gain for 4G and three 5G signals in the frequency range from 780 MHz to 26 GHz, coexisting in the transport network. The obtained digital performance has efficiently met the Third-Generation Partnership Project requirements, demonstrating the applicability of the proposed approach for using fiber-optic links to distribute and jointly amplify 4G and 5G signals in the optical domain.