I'd disagree with Bob. It seemed to me to be a lot like Gabon was cast and planned to force an older winner more than any season until Nicaragua - nearly a quarter of the cast was over 45, he and Gillian were the only ones with anything resembling survival experience, the challenges weren't too physical (and those before the merge that were physical often had a puzzle component he worked on instead), and most of the younger people were so obnoxious they cancelled each other out.
Maybe Vecepia? Or Jenna?
I think what really made Bob unlikely was the decision to allow the cast to pick their own tribes, and TPTB constantly bailing out Fang for constantly making stupid decisions. I thought Bob was a pretty likely winner with a few episodes remaining though, provided he could get there, because Susie herself threw away any chance she had of winning the game and the jury wasn't going to vote for Sugar anyway.
Jenna's game was very unappreciated. Vecepia is probably the most unlikely winner because she did everything in her power to throw the game away at every turn. She made so many huge errors but was able to survive them time after time. I know she's tried to get back onto the show for a long time but I'm glad that casting hasn't pulled the trigger. Chris, too, has been trying to play again this entire time and I'm shocked that they never brought him back. He's honestly one of the best winners ever, severely underrated, and would probably be a lock to go deep in any season because he's just physically useful enough to not be deemed a challenge liability.