Wi-Fi and Bluetooth grayed out on iPhone

This would indicate the chip that houses Wi-Fi and Bluetooth has failed in your iPhone. As a result you need to have your iPhone serviced at your nearest Apple Store’s Genius Bar or Apple Authorized Service Provider.

Genius Bar Reservation and Apple Support Options - Apple

It would not hurt to try a Forced Restart......but it also probably won't help.

Unfortunately, when both Wi-Fi and Bluetooth are grayed out, this is an indication that the chip that controls both of these services has failed.

The iPhone will require service at the Apple Store / Genius bar or a local authorized Apple service shop.

Given the age of the phone and the cost that would be incurred to replace it, it might be a good idea to consider a new device that will support the newest iOS.