Was helping someone out recently with getting their iPhone set up to download apps. They had the phone for a while but only used it as a phone (they aren't tech-savvy). We couldn't even install the Kroger (grocery store) app because it said it required iOS 11, and she was still on 10.

She was not given the option to download an older version compatible with iOS 10 and the device is old enough that it does not support iOS 11.