[OKSooner]

"Estimated to be 13 billion years old..."

To paraphrase, "A billion years here and a billion years there and pretty soon you're talking about some real time..."

How did they get there in the first place? [friendly /s]

[SunkenCiv]

Here’s a good summary:

http://www.scientificamerican.com/article/how-do-scientists-determi/