While configuring a reference bandwidth (which is used to calculate link costs) can be useful, it is not strictly required for IS-IS to run. IS-IS uses default bandwidth values to calculate costs, and it can function without explicitly configuring a reference bandwidth.

In the configuration on router R1, the static route is defined with the next-hop IP address of 139.120.121.1.
However, the next-hop IP address 139.120.121.1 does not belong to the same subnet as the directly connected interface on R1, which is 172.31.1.1/30. For the static route to work properly, the next-hop IP address must be reachable via a directly connected interface, meaning it must be within the same subnet.
Therefore, this mismatch in subnet adjacency is likely causing the failure to reach the destination (139.120.121.2).

When a router receives a link-state advertisement (LSA), it does not update the age field before forwarding it. The age field in an LSA is typically updated by the originating router or during the process of forwarding the LSA within the network. Routers do not modify the age field upon receiving and forwarding an LSA.

From the route tables of R3 and R4, we can see that remote routes are present, with R3 and R4 both having routes referencing routers in different areas (Area 49.01 and 49.02). These remote routes are characteristic of route leaking, which is the process of sharing routes between different IS-IS areas.
R3 has routes for R1, R2, and R4, which are in Area 49.01, suggesting that R1 and R2 have advertised their routes to R3, possibly due to route leaking.
R4 has similar routes for R2 and R3, indicating that R2 might have advertised its routes to R4.
This sharing of routes between areas is indicative of route leaking being configured on both R1 and R2, allowing these routes to be shared across the areas.