Complex sentence: Gottheimer attended the University of Oxford for a year following Clinton's reelection joined the Clinton administration as a speechwriter in 1998, at the age of 23, and served the administration until its end in 2001.
Split into simpler sentences: Gottheimer attended the University of Oxford for a year following Clinton's reelection. He joined the Clinton administration as a speechwriter in 1998, at the age of 23, and served the administration until its end in 2001.