Immortality isn't happening, but you can significantly increase your health-span, to give you more time to keep learning cool fascinating stuff. There are steps you can take now to delay aging, based on well-run clinical trials, including supplementation with metformin (the TAME trial). Other measures are looking hopeful but are still being researched, including use of rapamycin (PEARL trial). Here's a good resource: a podcast by Dr. Peter Attia, also good for nerding out on lots of interesting topics. https://peterattiamd.com/podcast/

Are there any experts in life-span extension? Or, maybe what you meant was longevity extension - are there any experts in longevity extension? (Life-span extension means avoiding early death, longevity means being able to live longer than any humans have ever lived, say, 200 years or whatever.)

I’ve read a bunch of pseudo-science and heard about so-called “experts” claiming it’s possible and coming, but the field seems to attract charlatans promising immortality…

If new things to be expert in proliferate faster than you can become an expert then life-span extension will not work. You would need to duplicate yourself each time there is a new thing you want to pursue. One you would be a concert violinist and the other you could cure the common cold.