What we know:
It is 1400 light-years away from Earth.
It orbits a star called Kepler-452b.
Its star has about the same temperature and mass as the Sun, and 20% more luminous than the Sun.
What we kind of know:
It is about 60% bigger than Earth.
It could be as much as 5 times more massive than Earth. It is very difficult to determine the size and mass of planets that far away. Our telescopes and computers and not yet that accurate to determine the mass of exo-planets smaller than Jupiter.
What we don't know:
We don't know that it is 6 billion years old. That number is based on rough assumptions based on even rougher assumptions.
We don't know that it is a terrestrial planet. It could be a small gas planet.
We don't know if it offers a habitable environment.
We haven't heard from aliens on the planet. As a matter of fact, we don't know if there is any life there.
The bottom line:
The Kepler telescope, whose mission is to look for planets around other stars, has discovered a dot orbiting a star far away. The dot's size-distance relationship with the star it is orbiting makes it the 6th most Earth-like object in space discovered so far. Planets Kepler-438b, Gliese 667 Cc, KOI-3010.01, Kepler-442b, Kepler-62e, are believed to be more similar to Earth than this planet.
Sources:
NASA, Wikipedia