Hello Sasindu
The link-state age field is reset every time a new LSA arrives. The maximum age of the link-state age field is 30 minutes. After 30 minutes if no new LSAs arrive, any existing LSAs are considered invalid. For this reason, LSAs are resent every 30 minutes.
However, the link-state age field is reset every time a new LSA arrives.
Keep in mind that in a stable OSPF topology, no new LSAs will be sent. For this reason, it is likely that you will see LSAs expiring and being resent after 30 minutes.
I hope this has been helpful!
Laz