From your link:
So in a general sense, adiaphora means those Christian teachings which are neutral, things that are neither commanded nor forbidden in Scripture. An example of this might be what color of carpet to have in a church, or what time of the day a service should be held. Sometimes there is debate within Christianity on what may or may not be adiaphora.
I don't think this issue is an adiaphoron. While the 6k age is something man-made in that it isn't commanded or forbidden in scripture, creation is described there.
Im sorry you feel that way but the age of the Earth has no bearing on my salvation. The Bible also describes man being formed out of dust - but does not discuss the staggering complexity and nanotechnology of the living cell, and the digitally-coded information content of DNA. I also will not deny DNA and claim it is really dust but I will marvel at Gods creation.