With increase in real-time systems, users have come to demand information with low latency. However, as the blocklength becomes finite to reduce communication duration, the decoding error probability is newly considered. In this letter, we consider downlink cellular networks, where s (s) periodically transmit information with finite blocklength to a user. To analyze the freshness of information, we derive the average () and the violation probability in a closed-form using the upper bound of the average decoding error probability. Finally, we show that an optimal blocklength that minimizes the exists.