Comment by zarzavat

Just make enabling jailbroken mode require a factory reset of the device.

The biggest risk is not elderly people but rather the owner giving their passcode to someone else, e.g. a repair shop, who then enables jailbroken mode without the owner's knowledge and installs malware.

You can mitigate this problem, and the elderly person problem, by requiring the phone to be factory reset. That way any jailbreak would be extremely obvious.