A 3D printer is certainly a very useful and interesting hobby. For starters, you can use ready-made models (for example, there are a lot of them here https://www.thingiverse.com/). But until you learn how to model, it won't be more than just a hobby. Try to start with simple modeling programs (eg https://www.tinkercad.com/) and then move on to a higher level, such as AutoCad. By learning 3D modeling you can start planning a small business. Good luck to you!