In other words, if you're pulling in e.g. regenerator-runtime, you're already cutting out a substantial part of the users you're describing.
So that's my cutoff.
Android Studio has a nifty little tool that tells you what percentage of users are on what versions of Android. 99.2% of users are on Android 7 or later. I predict that next year, a similar percentage of users will be on Android 8 or later.