“And old” what?
If you have an old house, that has plaster walls – that can impact Wi-Fi signal. Plaster is essentially concrete. On walls it’s more impactful to Wi-Fi than drywall (sheetrock).
Any electrical motors (refrigerant compressors) will impact Wi-Fi.
Metal studs in the wall impact Wi-Fi.
Impact windows (hurricane windows) impact Wi-Fi.
I have an small older home in the SE USA that has “stucco” on the interior walls. Stucco is essentially the same as plaster. Wi-Fi coverage in my tiny ~1500 square feet home is not great.