You say that yet you do not enumerate how they are different. I see lots of similarities between boats and spacecraft, some pointed out above. How do you see they are different?To cross the oceans and to do space flight are two fundamentally different kind of things with fundamentally different requirements because of its fundamentally different environments. Such comparisons do not make any piece of sense.
I think you are seeing the limitations of the human body and not considering the technology that may overcome them:As for the increase in lifespan:
some people have too much expectations and a too optimistic view on that. The increased lifespan doesn't have anything to do with immortality or going to become so. Beyond the 80 years, quality of living and happiness decreases dramatically while diseases increase (mostly you'll get nearly blind or rattly and bedridden). About 50% of the ninety-year-olds in the industrial nations suffer from dementia. And if we talk about the magic 100 years, only ~0.012% of the Germans for example become 100 years old. While the majority of them are almost seemingly dead (at least they still breathe and gaze at the ceiling 24 hours a day, but they can't move and talk anymore). Those very few who still seem to do well are exceptions.
http://en.wikipedia.org/wiki/The_Singularity_is_Near
I consider Kurzweil's timeline wildly optimistic, and don't agree with some of his ultimate predictions (such as "abrogation of the laws of Physics, interdimensional travel"), yet I have trouble picking holes in the basic concept.