With perfect health and no loss of mental capacity? Probably Never. Too much to learn, do, see, and explore to ever give up....

Never say die.

Immortality, I think would have it's pluses and minuses. I really can't say, if I was able to extend my life I would want to be healthy. Very hard to say...watching everyone die. Being able to process all the change is difficult. I think Ann Rices books portray this beautifully. My answer is I do not know.

if i were well enough and my planet existed, never.

g

Interesting question, but one that also raises the question of privilege. The super-rich are indeed thinking of ways to prolong their lives indefinitely - and diverting our resources and tech know-how to that end.
In the meantime, growing numbers are being denied access to health care. Death rates of the poor, especially Native American are increasing. To fund the heavenly fantasies of super-rich (moon travel, immortality), environmental destruction, regime-change and wars are being waged on brown and black people around the world to gain control of their resources and markets.
In the middle, is the comfortable middle-class of Western nations. To get their support for the fantasies of the super-rich, our corporate media present those fantasies as if they are common human aspirations accessible to all.
It is indeed no accident that the most famous literary character who lives forever - Dracula - does so by sucking the blood of others!

I know. If we wipe out all the animals , I no longer want to be around .

And if hypothetically, we could live forever, I don't see humans, as a species, existing that much longer. So "forever" becomes moot.

When they run out of ice cream!

If you could live forever would not the concept of time be rendered meaningless? The notion of forever or eternity implies no beginning or ending.

When I stopped getting pleasure out of life...same as this mortal life I suppose

I'm not sure how I will feel about life in 20 years, let alone 20 million.

No. I have no way of knowing.

given the way the world is going, pretty sure it would be sometime before the environment becomes unlivable for everyone else, though.

Tomorrow afternoon seems as good a time as any.

I'm an extremely curious person. I want to know everything. I figure I could go at least 400 years without getting bored. If we break any new frontiers, it could be much longer.

This sums it up for me.

No

I'm certain that one could always find a reason to live one more day.

Ten years ago.

Yes
Exactly NOW

No.

I'm thinking somewhere around 250 years would be my limit, give or take depending on circumstances.

I'm already deeply tired of the human condition after less than 62 years. I am merely curious about how some things will turn out, and I might like to be a third-wave colonist someplace like Mars just to see what that's like. But on the other hand if the world degenerates into some kind of fascist dystopia none of that would be possible and I'd check out sooner. And if we made First Contact and were given a Great Leap Forward by some beneficent interstellar species, I might stay longer. It's very much like the decision whether to watch a TV series all the way to the end or not. (Or past season three where the last original idea was put forward).

It all depends how good my faculties would be. if I were blissfully unaware of having a loss of short term memory it would be quite a pain in the butt for people around me so I'd like ot get off before that happened

Excellent question and one I think religionists are afraid of. Living to 100 is easy. Try 1,000. That would be unimaginable. Everything and I mean everything becomes boring when it is repeated over and over.
I would answer not when I would choose to stop but how.

When I could no longer stand the stench of my own decrepit body.

Sure. Upon obtaining the ultimate bit of information to be had and having the final experience available. Until then: Rock on.