Middle Android Developers
It is a mistake to believe that there is a clear gradation depending on the number of years worked: so, with due diligence and work on a complex project, a junior developer can grow to middle in a year, and, conversely, a candidate can work on a project for several years and not move forward. Therefore, when searching for a middle developer, it is better not to focus on years of work, but look specifically at the experience and ability to work independently.
In general, the main difference between middle developers and juniors is that they already have experience working with complex Android-based projects and do not need dense mentoring like junior developers.