Update to iOS 11 ASAP
If you want to play Pokémon Go on your iPhone, then you must upgrade your device to iOS 11 as soon as possible. It is important because you won’t be able to access your account anymore after 28th February. So, if you want to use your coins and items in your bag, then you must upgrade your iPhone before facing any consequences.
Why will support drop for devices lower than iOS 11?
The developer revealed the reason behind dropping the support. “This change is a result of improvements to Pokémon Go that push the application beyond the capabilities of the operating systems on such devices.”