Answering this question is difficult because it really depends on a variety of different factors. If you are already well-versed in the skills needed to become a successful VA, then the time it takes to become one will be much shorter than someone who is brand new to the field. The amount of time you are willing to dedicate to learning and honing the necessary skills is also a big factor.
If you are starting from scratch and want to become a VA for Amazon, it would be best to first gain a comprehensive understanding of the skills necessary for success which would involve studying Amazon Marketplace and services, understanding how to use Amazon Seller Central, gaining knowledge of strategies for listing optimization and understanding marketing fundamentals. You would likely also need to learn other important skills such as how to communicate effectively with clients and how to manage projects.
Getting certified in Amazon services can also potentially improve your chances of being hired as a VA. Once you've gained a comprehensive understanding of Amazon services and have meaningful work experience, it will be much easier to pass the certification exams. This could potentially shorten the time you need to become a VA.
All of these factors will be dependent on how much time and effort you are able to dedicate to gaining the necessary skills and knowledge. If you are dedicated and have the right attitude, it is possible to become a VA within a few months. However, you must both invest the time and persevere through any challenges that might arise.