https://astralcodexten.substack.com/p/book-review-lifespan

[epistemic status: non-expert review of a book on a highly technical subject, sorry. If you are involved in biochemistry or anti-aging, feel free to correct my mistakes]

David Sinclair - Harvard professor, celebrity biologist, and author of Lifespan - thinks solving aging will be easy. "Aging is going to be remarkably easy to tackle. Easier than cancer" are his exact words, which is maybe less encouraging than he thinks.

There are lots of ways that solving aging could be hard. What if humans worked like cars? To restore an old car, you need to fiddle with hundreds of little parts, individually fixing everything from engine parts to chipping paint. Fixing humans to such a standard would be way beyond current technology.

Or what if the DNA damage theory of aging was true? This says that as cells divide (or experience normal wear and tear) they don't copy their DNA exactly correctly. As you grow older, more and more errors creep in, and your cells become worse and worse at their jobs. If this were true, there's not much to do either: you'd have to correct the DNA in every cell in the body (using what template? even if you'd saved a copy of your DNA from childhood, how do you get it into all 30 trillion cells?) This is another nonstarter.