Best way to become biologically immortal is probably to solve aging directly in your own body via some sort of whole body viral gene therapy.

Then your still mortal and can be killed so you can chose when to go.

My person preference for immortality would be some sort of live un-interupted transition from a human brain to a computationally simulated one. Only if I personally own my own infrastructure though. That way I can ensure I don't get manipulated. Then probably copy my conscious 100x over and spread over geographically. Maybe keep a copy in a extra solar satellite or something.

I mean as far as startups go its about on par making one about creating replicators but senescence is actually a good thing and we do keep on making cells. With everything else being young and healthy its possible the blood and organs will clean out detrious (like senescent cell) and allow for better creation of new cells. Im not saying it would last forever but it could possibly go much longer.

Usually you want more than you get, though.

SciFi can be interesting, but the pursuit of immortality or even extensive longevity always seemed to me like a very very bad idea to me. I like living, I don’t like living enough to want to do it forever.

Myself, I always saw the point of the pursuit of immortality to not actually be immortality, but letting you choose when you're truly done with the world rather than dying of some arbitrary cause out of your control.

Some might decide they're done at 70 years, some at 700. The societal changes needed to make it work would be immense, but wresting control of your death date from luck and nature into your own hands seems a worthy enough goal to me.