Since this year you won't be allowed to do that anymore - since backwards compatibility behaviour allowed app developers to avoid privacy protecting features like runtime permissions.
I'm not an Android developer but they say supporting older versions should still work:
"Existing apps that are not receiving updates are unaffected. Developers remain free to use a minSdkVersion of their choice, so there is no change to your ability to build apps for older Android versions."
Yes, you can still support older versions. But the app must target at least Oreo, which means supporting the new permission model on newer versions of Android while making use of unfettered access on older versions.
