For the iOS mobile platform, Apple already stops supporting 32 bits apps, but in the case of the macOS the transition to 64 bits will be slower and will start in 2018. It seems that the new macOS High Sierra will be the last to offer support for native 32 bits apps and the future versions will come without support for the obsolete software.
In what iOS is concerned, Apple no longer accepts 32 bits apps in the App Store and encourages developers to update their apps before the official launch of the iOS 11 operating system. After the release, the apps will be removed from the App Store and those that are installed on devices will stop working and this scenario will happen again next year when the macOS High Sierra operating system arrives.
Starting with January 2018 Apple will no longer accept new 32 bits apps in the app Store and updates for existing apps, to switch to 64 bits, will be uploaded in the app Store before June of 2018. Most likely, after this date, apps that do not comply with the new rules will be removed.
It is not clear what will happen with the 32 bits apps that were installed outside the Apple Store but most likely with the launch of the High Sierra operating system, all 32 bits apps will stop working.