Complex sentence: He also served as Director of Welfare in Vlaardingen from 2000 until December 1,2001, when he became Mayor of Noordwijkerhout, he was the youngest Mayor of the Netherlands at the age of thirty-eight.
Split into simpler sentences: He also served as Director of Welfare in Vlaardingen from 2000 to 1 December 2001, when he became Mayor of Noordwijkerhout. Upon his appointment, he was the youngest mayor in the Netherlands, at the age of thirty-eight.