Yes it will work on newer versions as long as you do not have maxSdkVersion
set to 21
In your application manifest, you will find up to three attributes:
android:minSdkVersion
android:targetSdkVersion
android:maxSdkVersion
If your max is set to 21 then it will not work with newer versions. You might not even have a max set.
You likely have your target set at 21 or your min set at 21, or both...
You can learn more about <uses-sdk>
here
One thing to note : 4.4 kitkat still has 17% of the API distribution so you might want to set your minSdkVersion to 19. You can find a weekly updated distribution chart here