Information freshness is a crucial metric for time-sensitive services such as Basic Safety Messages (BSMs) in Vehicle-to-Everything (V2X) communications to achieve high-reliability autonomous driving. However, Semi-Persistent Scheduling (SPS) algorithm under the current 5th generation (5G) New Radio (NR) standard may not fulfill the requirement of such a metric for BSMs without optimizing relevant parameters. This paper analyzes the parameters of SPS used for BSM scheduling in NR-V2X Mode 2 from an Age-of-Information (AoI) perspective, to explore the freshness of BSMs. We first present an analytical model to illustrate that Resource Reservation Interval (RRI) is the SPS parameter which significantly impacts the AoI performance. Subsequently, we investigate the expected peak AoI (PAoI) performance with respect to RRI values under different vehicle densities. A Monte Carlo simulator is then utilized to verify the results obtained in the analytical models. Numerical results show that the optimal RRI values in SPS, which minimize the expected PAoI of the vehicular network, can be obtained based on different vehicle densities accordingly.