[hakanderyal]

I started with a command line calculator when I was 17(Internet was a luxury for me back then.)

You can try your hand at algorithms. You can implement them in a language of your choice, try different methods, try to speed things up etc.

If you are in to math, you can try projecteuler.com, it is a good learning source, provides lots of interesting problems to solve.

You can check code katas. https://en.wikipedia.org/wiki/Kata_(programming)

The idea is not that important at first. By doing even simpliest things, you will expand your knowledge on programming, which in turn will guide you about what you can do with it.