In what can only be described as yet another stupid move for Niantic, they have announced that Pokémon GO will no longer support Apple devices that can not run iOS 11. Players that have an Apple device than cannot run iOS 11 but can still currently play Pokémon GO will become obsolete on February 28th, 2018.

Pokémon GO to discontinue support on Apple devices that are not capable of upgrading to iOS 11

Trainers, In an upcoming update to Pokémon GO, we will end support for Apple devices not capable of upgrading to iOS 11, such as iPhone 5 and iPhone 5c models. This change is a result of improvements to Pokémon GO that push the application beyond the capabilities of the operating systems on such devices. This change will take effect on 02/28/2018. After that date, Trainers using affected devices may no longer be able to access their Pokémon GO accounts from that device, or use their PokéCoins or other items in their Bags. They will need to switch to a supported device to continue playing Pokémon GO. You can see the full list of impacted devices and learn more by visiting our Help Center.

Source: https://pokemongo.nianticlabs.com/en/post/iphone5discontinuedsupport