Hi,
Allan Jones is of course right. A plain iPhone 5 (it may not work with anything higher than iOS 10) is completely outdated as far as modern applications are concerned. However, it will still work with the original Apple apps, and it is possible to use it for telephone calls and SMS. The camera is not bad. Connected to a Wi-Fi router, the phone can even be used for very basic web browsing, albeit slowly, ... and who needs Facebook?
So, I would suggest that you go ahead. Make sure that the iPhone has been erased and returned to its "factory settings" via the steps in the above Apple article. Tell the recipient about the limitations, and then let her/him decide whether or not those are important. Good luck!