Complex sentence: In 1953 he conducted the Berlin Philharmonic Orchestra, becoming the youngest person ever to do so, and when he debuted at the Bayreuth Festspielhaus conducting "Tristan und Isolde" in 1957, he was the youngest conductor ever to appear there as well.
Split into simpler sentences: In 1953 he conducted the Berlin Philharmonic Orchestra, becoming the youngest person ever to do so. When he debuted at the Bayreuth Festspielhaus conducting "Tristan und Isolde" in 1957, he was the youngest conductor ever to appear there as well.