This read-only INTEGER reports how many seconds have elapsed since this forwarding-table sub-entry was inserted into the NFFT. It's useful for spotting stale or unexpectedly long-lived entries versus ones that are churning and being reinserted rapidly, which can indicate route flapping or an aging-timeout misconfiguration. An admin noticing forwarding instability for a destination could poll this age value repeatedly to see if the entry keeps resetting to near-zero, confirming rapid re-learning.