The world changes fast, and the rate at which it changes is itself speeding up. In such a world it's not a good idea to have fixed plans.
Architects know that some kinds of design problems are more personal than others. One of the cleanest, most abstract design problems is designing bridges. There your job is largely a matter of spanning a given distance with the least material. The other end of the spectrum is designing chairs. Chair designers have to spend their time thinking about human butts.
It's not so important what you [high school students] work on, so long as you're not wasting your time. Work on things that interest you and increase your options, and worry later about which you'll take.