Sinclair is ok. He wrote a book called “lifespan” that’s pretty well regarded. Also look up Aubrey de Grey. His book, Ending Aging, is also good. He himself is problematic though. If you’re interested in this sort of tech, also look up the SENS foundation (I donate there).
Fair warning, most everything focuses on increasing healthspan, not lifespan. I.e. Being able to be active and alert at 90. There’s no way for tech to guarantee an increase in lifespan within our lives, because we would need a few generations of evidence to guarantee that. So at most you’ll get partial evidence and animal models. But you gotta start somewhere. And if we’re lucky, we’ll stop be around for the ‘proof’ in 200 years :-)