I don't think it's a bad thing to be a bit afraid. Listen and learn from your fears.
Let's be honest here... you're 55 years old and all your wealth to date has taken a LONG time and a tremendous amount of effort to create. It's not something you want to lose, and it's not something that can be recreated overnight. When getting into something new, it's always sound advice to take on a mentor... or several. This will help you learn in a positive environment and would theoretically reduce your risks. The Bay area isn't inexpensive either... you're going to have a lot on the line, with varying degrees of exposure.
I suggest you play it smart. Partner with someone who has a proven track record of doing flips. Spread the risk and share the rewards/potential downside. Do this under an LLC so that if ALL HELL breaks lose, what's left of your personal nest-egg is protected.
Most people aren't in the same financial situations... some can stomach losing 5K, some 500K, some 5 million, etc. Choose what you are comfortable loosing. No investment is a 'sure thing', so be prepared to take a few hits before you figure it all out. Figure out what you're comfortable with, and figure out how to do a deal with that amount of exposure.
Take calculated risks, choose good and experienced people, and work through the learning curve.
Best of luck!