if you lived sat a trillion years the restof the human race would be extinct, and so there would be nothing to live with. and another thing: when you are 80 you are very frail and weak. imagine how week you would be if you were a trillion years old. there would be nothing left of you. and as pararealist said above, after a while you would loose it anyway, so there would be no point. and if you are immortal can you commit suicide?
I guess with immortality would logically come the conclusion that you would not age. So being frail and weak wont be a problem. And anyway there are plenty people who are old as dirt and still are fit as a fiddle.
After the first 10,000 years or so one would probably go crazy anyway, if not sooner.
Well, that is subjective too. Depends on the person, but yes, after some time one would go crazy too.
I think a good lifespan where you would have time to do really everything you "wanted" to do (not "can" do) would be something around 1000 years.
