I am on an old MacBook (mid-2009) that is not supporting Sierra. When I go to the App store to install Xcode 8 (only option available) it says that it is for 10.12 (Sierra) only. That means that if someone has El Capitan only and didn't install Xcode 7 before, cannot start developing apps for macOS / iOS? That seems absurd to me, El Capitan is still a modern OS... I might understand if you are on Leopard, but El Capitan is from 2015!
Is there any way to (legally) bypass this problem?