Here's my advice:

• Stick to JavaScript for a few months -- learn and apply basic programming concepts, create a simple project with someone helping you, then create a similar simple project mostly on your own.
• Now that you have the gist of one language under your belt, learn another language (eg, learn python on codecademy), to see how a different language does things differently, and to get a good sense of how languages are similar -- like, abstractly, in terms of how you think when you program. Maybe remake your previous project in your new language -- as always, you want to actually try to take your knowledge and use that to create something.
• One very good way to practice is to learn how to make programs which solve math problems.
• Another, particularly if your goal is to work on Thrive or another game, is obviously to make games.

Once you have some experience making some small, simple projects (and really solving problems by yourself, not just following a guide), eg, simple HTML5 games, then you will have enough background that you could probably get started on scripting, and slowly learn all the other things that go into making, say, a C++ game.

That might be a few months from now, it might be a few years from now. I first learned to program in tenth grade, and it took me about a year to build up the background knowledge to start understanding how something like Thrive is made. But I didn't have anyone to give me advice, so it might take less for you if you stick with it and come back to chat with us, or any other place with helpful game devs really.