Lewis Hamilton won the 2008 F1 World Drivers' Championship at age 23 years, 300 days, making him the youngest champion at that time. Fernando Alonso was slightly older when he won his first title in 2005. The record was later broken by Sebastian Vettel in 2010 (age 23 years, 134 days), but based on the available options and the temporal context of these questions, Hamilton is the intended answer.