join a game company as a junior. Hate every bit of it and then realize you're better off doing something else.
Or skip all of that and pick something you are somewhat familiar with today.
If you're still reading that means you want to continue on this treacherous path. Fine, fastest way to start i guess is playtesting but with companies asking customers to do that for them.. the role is kind of lacking at the moment.
best you can do in your free time is start with trying out every aspect of game design upto a beginner level: learn basic coding in a specific language like python. learn to make simple text based adventures and fill-in-the-blank puzzles.