The danger of taking a look at SFML so early is that you get fascinated by game programming and neglect C++ itself. SFML is quite beginner-friendly, but to use it efficiently, you still need to have knowledge of advanced C++ concepts. It is possible to achieve cool stuff with few C++ knowledge, but your applications are likelier to have bugs and run slowly and unstable.
If you know the basics (control structures, functions, classes, pointers), you can approach SFML. But I recommend to continue learning C++ steadily. Some very important concepts that are not treated in many books are RAII (or how to avoid manual memory management), templates, and the STL with its containers, iterators and algorithms. Also C++11 becomes more and more important, but most of it concerns advanced topics anyway.
In any case, you should have a good C++ book. Unfortunately, there is a lot of bad literature, a good list can be found
here. Note also that after learning the basics, you should take a look at a book teaching good C++ practices like Meyer's Effective C++. By applying the read knowledge in your projects, you also get practical experience, which is a very important part too.
And don't look at other's game code, except you know it's really well written. Unfortunately, many game programmers use an awful C++, based on antiquated techniques, myths and plain wrong understanding. They eventually still create good games, but they develop longer, debug longer and maintainance is a bigger pain. SFML is a notable exception, it is one of the best designed C++ libraries I have ever encountered.
