https://www.youtube.com/watch?v=LERAgcuv8jg

Date:
January 8, 2020
Source:
Mount Desert Island Biological Laboratory
Summary:
Scientists have identified synergistic cellular pathways for longevity that amplify lifespan fivefold in C. elegans, a nematode worm used as a model in aging research. The increase in lifespan would be the equivalent of a human living for 400 or 500 years, according to one of the scientists.
https://www.sciencedaily.com/releases/2020/01/200108160338.htm

Milbank Q. 2002 Mar; 80(1): 155–174.
doi: 10.1111/1468-0009.00006
PMCID: PMC2690099
PMID: 11933792
Extending Life: Scientific Prospects and Political Obstacles
Richard A Miller
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2690099/

Pushing Limits of the Human Life Span
By Gina Kolata
March 9, 1999
Future generations, they said, may be able to avail themselves of scientifically established techniques to stretch the human life span like a piece of taffy until it reaches 150, even 200 years.
https://www.nytimes.com/1999/03/09/science/pushing-limits-of-the-human-life-span.html

I don't recall the source or the article title but I remember reading about how as we age, our cells (er, DNA or something) breaks down like a copy of a copy of a copy of a copy. Eventually the resolution gets so bad you can no longer make out what the original was.
If that breaking down over time by copy were to be halted, cells would regenerate pristine. If your cells regenerate pristine not only would you not age, you would grow back lost teeth and your eyes, skin, hair, etc would regenerate. I can't recall which science site I read this, might be Foresight Institute or another transhumanism site.

I also read in Drexler's Engines of Creation about how nanotechnology could one day repair cells causing death to be obsolete.

The problem with very long life is the fact humans love to reproduce. We would need a new planet or two very quickly. There's already more people being born than dying every minute. It would get really crowded, really fast.