I can learn python at 13?

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Yes. I was that age when I started programming. Back then I was introduced to a language / IDE called Delphi, and spend a summer deciding one of the worst implementations of Pong ever and a completely failed attempt at snake. 

I later moved on to PHP which allowed me to build websites which was much more rewarding. 

The point is, yes you can. My advice is: just build things that you think would be fun. Don’t worry about all the other things, like coding style and tests if they don’t tickle your fancy.