No, it's not - lots of people have mastered Android. Android is just a different execution environment for your Java code, with its own GUI and architecture. In that sense it's not so different from Java desktop development or Java web development - both of which come with their own GUI and architecture as well.
New to android development.I have some experience with java.
Is it too much of a learning curve?
Also which language is better suited java or kotlin?
And in a year or so (when Head First Kotlin is out...) you will be able to take your knowledge of the underlying Android concepts, and express them more concisely in Kotlin
Head First Android Development
Besides reading books like "Head First Android Development" Another essential resource is Google’s Training Resources
For Android App Developers.
Google has created an Android Developer portal where you can get everything you need to start creating your first Android app.
On this website, you can download the Android Software Development Kit (SDK), take Android video classes, read their blog and
access extensive Android Development resources.