Currently the Oppia app supports versions of Android down to ‘Ice Cream Sandwich’ (Android v4). This was released in Oct 2011 - so is over 8 years ago now. See: https://en.wikipedia.org/wiki/Android_version_history
Supporting very old versions of Android makes things tricky for the code maintenance, so we’re considering making the minimum supported version to be Lollipop - Android v5 - released in Nov 2014, so is still a 5 year old version of Android.
Before we do this though I’d be interested to know if this might cause any problems for current implementations. @hakimks and @SidraRiaz - I’d be particularly interested to get your thoughts on this.