Supported versions of iOS, macOS, and watchOS
iOS - 9.3.5+
Support for iOS 9 & iOS 10 will likely be dropped in 2018
macOS - 10.11+
Support for macOS 10.11 will be dropped in 2018
watchOS - 2.0+
Only so many versions of an operating system can be reasonably supported without interfering with development of new features and maintenance. Apple is more than generous when it comes to supporting new versions of their operating systems on old hardware. It is always recommend that you run the latest public release that can run on your device.
