The age of the earth is not a salvation issue, in that we are agreed. However, if you doubt Genesis, how can you believe Jesus, the man, created all things? Or that he rose from the dead after 3 days?
Which other parts of the scripture do you think are "minor detail". Are you suggesting that the genealogies written should be ignored as irrelevant or incorrect? If you ever added them up yourself, and read the scripture exogetically, not eisogetically, you would come to the same conclusion re the age of the earth. You may then dismiss that conclusion based on "science so called". Perhaps you dismiss 1 Timothy 6:19-21 as a minor detail, and no warning at all?
Biblical genealogies could be accurate and there could still be an Old Earth. According to some Torah scholars, the first seven days of Creation are not counted in the number of Judaic years (currently 5776). This leads to a possibility that the “days” of the Creation are more like eras, particularly when you consider that the sun didn’t appear until several days into the process.
http://www.geraldschroeder.com/AgeUniverse.aspx
Also, this leads to the possibility that the Biblical Adam was not the first Homo sapiens, but instead was the first one with a soul.
http://geraldschroeder.com/wordpress/?page_id=79#h5