Let me start by mentioning that it is great to start thinking about a particular career track so early in your life. That being said, since you have a huge amount of time available , its better to start from the absolute basics. I would suggest Linear Algebra , Statistics and Calculus should be your beginning points.
Then moving on to the basic theoretical concepts of Machine Learning and Data science. The next steps should be understanding the basics of program development, visualization.
I would personally recommend that you refrain from focusing all your energy on one particular language. Considering the rapid change in the world of coding, the language that you are focusing all your energy on, may become obsolete in a few years time frame.
Of course, you will need a particular coding language for actually practicing all that you have done. For the same purpose, I would recommend Python as it is an easy to use language considering the vast variety built in libraries which can help you focus on the actual Machine Learning logic without spending too much time on the actual coding language itself.
Hope this helps. Please make use of the various MOOC platforms available for the courses. Happy Learning!