Complex sentence: Walker began his career on Wall Street when he joined Goldman Sachs in the Merger Department in 1992 and six years later, in 1998, became of one of the firm's youngest partners ever.
Split into simpler sentences: Walker began his career on Wall Street when he joined Goldman Sachs in the Merger Department in 1992. Six years later, in 1998, Walker became one of the firm's youngest partners ever.