Humans are physically and intellectually limited.
But on the verge of being able to redesign their bodies to do anything they choose; the brain is the weak point because it's made of goo rather than silicon or nanotech.
There are probably people alive today who'll get to see the heat death of the universe; assuming we don't wipe ourselves out, we're probably within a few decades of immortality (i.e. lifespans increasing by at least one year per year).
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No matter how advanced our technologies are today and will become in future, it won't ever be easy and cheap to go into space.
Five hundred years ago people would have said the same about crossing the Atlantic: the idea of flying across it faster than a musket ball for a few days' pay would have seemed absurd to them.
I remember Duncan Lunan, in one of his books, showing how you could theoretically lift a spacecraft from Earth's atmosphere and deposit it on the surface of Mars without using a single gram of propellant (though I suspect in the real world you'd need at least some for mid-course corrections). Of course you'd need a fair amount to set up the system of rotating tethers required to do it.
Other than our lower earth atmosphere, our oceans, our streets and railroads, space is and always will be a terribly unforgiving environment humans are not made for and not adaptable to.
Actually, free space is far more forgiving than many environments on Earth. Sure, humans need support to live there, but if you're coasting along with your engines off in between planets there isn't much that the environment itself is going to do that would harm you; solar flares are the most likely, with micrometeroids probably second behind them. Neither is as big a risk, if your spacecraft is properly designed, as facing a hurricane in a boat, or living a thousand feet below the surface of the sea.