Where is the minimum supported SDK version of coroutines-android stated? Is there such a restriction?

At least 14. The example project in the coroutines library uses that as the min SDK. https://github.com/Kotlin/kotlinx.coroutines/blob/master/ui/kotlinx-coroutines-android/animation-app/app/build.gradle.kts

I don't think there is an android version requirement for coroutines to work.