Native Android Apps are written using Java. You need to have enough knowledge of Java to ensure that you can write a decent Android Application.
You can use the following check list to ensure you have enough Java skills:
1. Can you write a Java class?
2. Do you know how to create an Object?
3. Can you create a method and invoke it from another class?
4. Can you read the API document?
5. Can you extend or implement?
6. Can you override and/or overload methods?
If the answer is yes to majority of the above, you have the pre-requisite to start with Android Apps development.