I'm a gold medalist in informatics (OBI), and medalist in physics, chemistry and math (2 times silver and bronze once in OBF, silver in OBQJr, silver in OBMEP) . Now, more then just to olympiads, I'm programming for fun.
At least for programming, the start is the most difficult part. So, if you want, one thing is a must: DO IT. The continuation will come naturally
After you start, you'll need to practice problems and make a site (this is the best way to master programming). To the problems, I have a recommendation: Neps Academy.
If you are interested in general science, I really recommend doing the Breakthrough Junior Challenge, it's an anual competition, and you can start prepearing to next year's right now.
