Xcode 9, support for older ios versions?

Question

iOS

Is there any way to support older versions of ios? I tried to add simulator files to xcode, I tried to install TestFlight on a device with firmware 4.2.1
At first I was delighted, I have an old macbook with xcode of a suitable version gathering dust at home, but the minimum version of the environment is 6 for publishing apps in the store :)
I will be very happy with any advice