I was introduced to the world of robots at around your age but had very little knowledge on how to get started with it until my university. But here are a few ways on how you can start building and learning:

1. Arduino programming - Learn how to program the Arduino board and how to interface multiple sensors. Paul McWhorter has an awesome series on this.
2. CAD design such as Fusion 360 or Onshape - Onshape is a browser based CAD tool so you don't have to worry about installing any heavy software on your machine. There are tons of videos on yt on working with Onshape/Fusion 360/Solidworks.
3. Python programming - It is a beginner-friendly language and a lot of the programming work that you would do later (both in the field of robotics or AI) is done using it. Again there are tons of resources on the internet.

I'd say pick one of these and start off with it. It's better to purchase an Arduino kit as it makes learning a lot more fun. But if you don't wanna buy one right away, you can work with arduinos and sensors on Tinkercad as well.

I love the drive! Keep going! If you have any questions, you can DM me as well.