Funders of a deep-pocketed new "rejuvenation" startup are said to include Jeff Bezos and Yuri Milner.Last October, a large group of scientists made their way to Yuri Milner’s super-mansion in the Los Altos Hills above Palo Alto. They were tested for covid-19 and wore masks as they assembled in a theater on the property for a two-day scientific conference. Others joined by teleconference. The topic: how biotechnology might be used to make people younger. Milner is a Russian-born billionaire who made a fortune on Facebook and Mail.ru and previously started the glitzy black-tie Breakthrough Prizes, $3 million awards given each...