Never, I totally believe I could handle living forever, as long as my body didn't age and make it very difficult lol. There are so many things I want to do, see, learn, experience. If humanity never changed then yeah it could get boring, but thankfully we evolve, cultures change, topics of interest expand, and how could that ever be boring?
Right now I have one little brief spurt of time in which to try to choose only what I can fit in with what time I have left, that makes me so mad.
An afterlife would be awesome, I don't want to cease to be, I want who I am to never die. Sadly I think we just die, that's us gone, but I like the fantasy of it.
I always imagined us coping with eternity. That we would somehow be different, I'd love it though. There are so many places I want to visit, so many things I want to do :( Just not enough time.
I myself wouldn't mind living for a few thousand years or so. That would give me plenty of time to do all the things I wanted to.
But people value their life and time because of how short it is, and because of what they want to do with it. If you had infinite time, then you wouldn't any more of it, as you don't need it.
But as I say, people only want time because they have things they want to do, and they fear that they won't be able to do them in the time the have.
Eventually, having done everything you wanted to do, which would happen eventually, you'd be left with the realisation that you've still got millions of billions of trillions of years to go. And, comparatively speaking, that's only a trillionth of a nanosecond of the time that you have left.
People like the idea of infinite time as they see it from their own limited perspective of having very finite time. Humans don't and can't comprehend time spans of this length, so understanding the difference between a mere human lifespan and eternity is not something that people are capable of doing.