Skeletons chase players and iron golems they see within 16 blocks, climbing stairs, navigating mazes and traversing other complex obstacles to get within shooting range. They can climb ladders if they are forced to do so. When within 15 blocks of a target, with a clear line of sight, they start shooting with arrows, once every second. If the player leaves the 15-block radius, skeletons wait for some seconds with the bow charged, shooting the moment the player comes within range again.

https://minecraft.fandom.com/wiki/Skeleton