In an effort to delay or possibly even reverse decrepitude, 45-year-old tech mogul Bryan Johnson has tapped his son's veins. Johnson sold his digital payments company Braintree to PayPal for $800 million in 2013, then started the brain-machine interface company Kernel. The technologist's millions reportedly did not bring him peace. Instead, he was left depressed, bordering on suicidal, haunted by the inevitability that the march of progress would one day leave him behind. TheBlaze reported earlier this year that Johnson had assembled a team of 30 doctors and was poised to spend $2 million a year on his body, admitting,...