Pokémon GO will no longer be supported on Apple devices below iOS 11 as announced earlier today by Niantic.
Trainers who haven’t updated to the latest version of iOS will no longer have access to Pokémon GO and their accounts as the upcoming update is scheduled to be release on 02/28/2018.
This change will affect Apple devices that are not capable of upgrading to iOS 11, such as iPhone 5 and iPhone 5c models. This is due to upcoming improvements which push the application beyond the capabilities of the operating systems on such devices.
Do note that after this change, Trainers who are still using an outdated iOS version will also lose access to Pokécoins and others items in their bags.
Unfortunately, there’s no work around this unless you decide to upgrade to a newer iOS device that supports iOS 11 and future firmware updates.