Age of information (AoI) is recently introduced to serve as a performance metric that quantifies the freshness of information for wireless applications with time-sensitive data. This paper studies AoI of wireless energy harvesting nodes in a multiuser cognitive radio network. In the envisioned network, primary users (PUs) and secondary users (SUs) coexist in such way that SUs harvest wireless energy from active PUs and access the primary spectrum opportunistically to transmit status updates. We model the distributions of PUs and SUs by a homogeneous Poisson point process and a binomial point process, respectively. We consider a greedy policy where each SU transmits an update whenever it harvests sufficient energy. A nonlinear energy harvesting model is used for SUs. Under the greedy policy, the average AoI of the secondary network is analyzed. An upper bound and a lower bound of the average AoI are derived. Simulation results demonstrate that the bounds closely approximate the average AoI.