This paper studies the collision-resolution random access (CRRA) protocol for information update systems with age of information (AoI) requirements. AoI measures the information freshness, defined as the time elapsed since the generation of the last successfully received update. When a large number of users contend and send update packets to a common access point (AP), conventional random access protocols such as slotted Aloha (SA) simply ignore the collisions and inform the users to contend for the wireless channel again, thus leading to high average AoI due to the high collision probability. This paper argues that resolving collisions can improve the information freshness. When a collision occurs in CRRA, only the collided users enter a collision resolution procedure (CRP) to contend and access the channel until all of their update packets are received successfully. In particular, the time to receive a user’s update packet in the CRP is random, which complicates the AoI analysis. This paper theoretically analyze the average AoI of CRRA. Simulations show that CRRA significantly reduces the average AoI of SA, especially when update packets have a large payload. Furthermore, CRRA is more robust against the estimation error of the number of random-access users, and it is thus a promising solution to networks with time-varying traffic. Copyright © 2022 IEEE.