Christian answering questions.

[snowtracks]

I don't see how a lack of proof for evolution - if we'd take that as a given for the sake of the argument - would lead you to a young earth.

It didn't. I became a Christian first and then learned about the Bible, God, young earth, etc and have confirmed it all since. My testimony makes it a little more clear how that is possible.

Young Earth all started when a certain group decided that to support science dating would be tantamount to endorsing evolution which would require epochs of time.  The book of scripture and the book of nature will agree since this is the means of how God reveals Himself.  The theories of science and the interruption of scripture may not agree, so in those cases,  the issue needs to be reexamined to resolve the differences. 
It took 3.5 billion years for the biomass in the crust of the earth to accumulate to be used by mankind; God gave the Genesis account of animal and plant preceding Man's arrival; this would be an example of scripture and science aligning. Why Man? Two main reasons for God creating the universe revolve around human beings (different then the animals, since they have been made in God's image, a spirit, therefore have eternal value): God's conquest of evil, and man's redemption.