Do you replace a router strictly by how long it has been on the market, or by how long it has been since firmware was released, or how long you have had it in service? It seems like a lot of the advice on the web advises to replace routers every three to five years.
I have two routers that were released in 2015. The last firmware update for both was 3/2022. Neither router is listed on the Asus End-of-life product list page. I only have two devices that can use Wi-Fi 6 or higher, so the older Wi-Fi 5/AC routers I have still meet my needs. Is there any other consideration I am missing ?