Android commands a large market share, but is also very fragmented. One of the things you'll want to consider when developing for Android beyond 90% of your demographic using Android vs iOS, is that you'll also want to figure out what is most common versions of Android that they are using...
For example, it would be pointless and a waste of time to develop an Android app that only supports 4.3 and up if majority of your demographic are still on 2.X.
Once you have the data you need on what versions of Android are most common versions of Android being used among your user demographics, it'll help you pinpoint what version of Android to target as a "minimum required".
Next you'll want to consider if that minimum version includes the necessary features and APIs you'll need to deliver on your app as well. If not you may have to move the requirements up.
These are things you'll need to consider when developing an app for iOS as well, but much less so as the adoption rate for the latest version of the OS is much higher for iOS than it is for Android (due to a large variety of hardware / OEM restrictions with Android handsets and manufacturers).