Conversation so far:
When did Mark Spitz' swimming career end?
Following the Munich Olympics
What was one of Mark Spitz endorsement deals?
Speedo swimsuit ads
What else did Mark Spitz do besides Speedo swimsuit ads  after his swimming career?
Mark Spitz started a successful real-estate company in Beverly Hills

Question: How long did his real estate career continue?
Self-contained rewrite: How long did Mark Spitz real estate career continue?