Thanks for the question. I understand that your Wi-Fi option on an iPhone 4S is greyed out. The following article explains this issue and potential resolution:
Follow these steps to resolve the issue:
1. Verify that airplane mode is off by tapping Settings > Airplane Mode.
2. Reset the network settings by tapping Settings > General > Reset > Reset Network Settings.
Note: This will reset all network settings, including Bluetooth pairing records, Wi-Fi passwords, VPN, and APN settings
3. Ensure that your device is using the latest software. To do so, connect your device to your computer and check for updates in iTunes.
4. If your issue is still unresolved, perform a software restore in iTunes.
If you are still unable to turn Wi-Fi on, please contact Apple for support and service options.