82 percent of all Apple mobile devices now run iOS 8.0 or newer

According to Apple, 17 percent of all active iOS devices are stuck running some version of iOS 7 (launched in September 2013), while just 2 percent of devices are currently running even older versions of the mobile operating system. Fair as these numbers may be, iOS 8 adoption is actually going a bit slower compared to iOS 7 adoption: around the same period last year, about 90% of all active iOS devices were running at least version 7.0 of the operating system.

Compared to Android, iOS is by a great deal faster in launching operating system updates to older devices, a feat that has a lot to do with Apple being the only manufacturer of iOS devices. Android is much more fragmented as an operating system, since Google itself can launch OS updates only to Nexus and Google Play devices, which represent just a fraction of all Android devices currently in the wild. Android device manufacturers are not as fast (nor as willing) as Apple when it comes to launching OS updates. According to the latest numbers from Google, just 5.4 percent of all active Android devices are currently running some version of Lollipop. Android 5.0 Lollipop was launched in October 2014. 

source: Apple