关联表问题

typedef struct
{
  UINT16 shortAddr;                 // Short address of associated device
  uint16 addrIdx;                   // Index from the address manager
  byte nodeRelation;
  byte devStatus;                   // bitmap of various status values
  byte assocCnt;
  byte age;
  linkInfo_t linkInfo;
} associated_devices_t;

查了好多资料，没有介绍这个age域功能的，求大神给详细解释下，谢谢！