A:Answer Depends on the capabilities of the older router, I have a mix of net gear and TP-link routers and extenders,.. The routers are all hard wired RJ45 connection. Only one is used as a router. All of the others are configured as access points. In a few locations I don't Ethernet wiring, so I have purchased 'extenders' which connect and repeat and pass through WiFi and also provide a RJ45 port for a wired/non-WiFi device.
TLDR: Need to dive into the documentation to see if your old router can be configured as an access point, and/or wireless extender. If not too old it probably can.