Scientists recently discovered an exoplanet named Kepler-452b which they state is "is 6 billion years old".
How did they determine this age? How could we possibly predict the age of any exoplanet?
I can understand estimates of size and orbit shape but age seems like a shot in the dark, errr, space.
To quote Jon Jenkins from NASA's Ames Research Center:
"It’s awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That’s substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet.”