In the summary of Noah on the lds.org site, it states that Noah was ordained to the priesthood at the age of 10 by Methuselah, his grandfather. Furthermore, in D & C 107:53, it indicates that the entire line of Adam from Seth to Methuselah were all high priests.
I understand that there are two priesthoods acknowledged by the LDS Church--the Aaronic Priesthood and the Melchizedek Priesthood.
The Aaronic Priesthood originated with Aaron during the Exodus. Melchizedek was a contemporary of Abraham, who lived a few hundred years after the flood.
Methuselah lived before the flood and apparently died the year of the flood, while Noah lived on both sides of the flood, of course, as did 7 other members of his family.
So, what specific priesthood did the line of Adam from Seth to Noah hold that would have to predate the other two priesthoods by at least four centuries?