This fall, Peter Thiel will celebrate his 54th birthday. He has already lived more lives than most mortals can imagine. He has been a Wall Street lawyer, a hedge-fund trader, a Silicon Valley entrepreneur, and a fabulously successful venture capitalist. The team he led at PayPal, the online-payments company he co-founded in 1998, is so influential in the Valley that its alumni are known as the “PayPal Mafia.” Zero to One, his provocative 2014 manifesto on innovation and start-ups, has sold more than 3 million copies globally. He was the most prominent tech titan to back Donald Trump in 2016 and remains a lavish supporter of Trumpish Senate candidates. Ambitious to avoid death, or at least postpone it, he has flirted with ideas for freezing brains for future reanimation and for transfusing the middle-aged with the blood of the young.