Does it work on an oldish Samsung tablet TAB4 (about three year old)?
Well, it works on Android 6 (Marshmallow) and above. I just looked up the TAB4 (http://www.samsung.com/uk/tablets/galaxy-tab-4-7-0-t230/SM-T230NYKABTU). If you buy one new, it will come with Android 7. So, maybe, your tablet is either running 7 now or could be upgraded to 7? If so, it should work on that.