Complex sentence: He debuted in the 2007/2008 season, and his big breakthrough came during the 2008/2009 season, where he, as of February 22 2009, has four podium finishes, including a gold medal in the 15 km mass start at the 2009 World Championships in Pyeongchang.
Split into simpler sentences: He debuted in the 2007/2008 season, and his big breakthrough came during the 2008/2009 season, where he, as of 22. February 2009, has four podium finishes, including a gold medal in the 15 km mass start at the 2009 World Championships in Pyeongchang.