If teenagers could make small contributions to LLMs via open source then sure, go for it. Optimizing llama.cpp or similar would be a good learning project that might later get you good work via social networks. Contributing to open source is how I got started too.
Unfortunately, training LLMs isn't something that fits well to open source open collaboration. Inferencing codebases are better.
In that sense it's more a "seek out the open source community and real projects when young" rather than "do web browsers", with a bit of "look for ambitious types of projects few get to work on".