RR Lyrae stars allow exact distance estimations and are found only in stellar populations more than 10 billion years old, for example, in ancient halo globular clusters. (sciencedaily.com)
I say «about» because I run for the fun of it and how it makes me feel after (and this year to train for the marathon again) so I don't know the exact distance. (joshuaspodek.com)
As for the answers to your other really, really uneducated questions: What caused us to be this exact distance from the sun? (religion.blogs.cnn.com)