No, we'd be straying off the path again if we headed up to Kohala. And as you've seen, there is only grass, cattle, and rainbows below Waimea. I'm not anywhere between the coast and Waimea. That doesn't leave much left for guessing.
Kohala is the oldest on Hawai'i, yes, but as you go Northwest in the chain, the age of the volcanoes increases. Kauai is 5 million years old, Kohala about half a million.
USGS page on Hawaiian volcanoes.
To sum up, this is what you guys have it narrowed down to:
