Complex sentence: He didn't know yet that there were different kinds at that young age but Marius knew what he was doing was some kind of an art and that he had fun and love doing it and so he never stopped since.
Split into simpler sentences: He didn't know yet that there were different kinds at that young age. But Marius knew what he was doing was some kind of an art and that he had fun and love doing it and so he never stopped since.