I think we corresponded a few years ago. Charles Cavanaugh is definitely Philemon Sr's eldest son and probably his eldest child. I do not see a 5 - 6 year gap between the age of Charles and Jael as a problem. At the most there would have been only 2 - 3 pregnancies between Charles and Jael. Miscarriages, still births and infant mortality cold easily account for the gap. One miscarriage and one child who died young could explain the gap. Disease could wipe out several young children in the space of just a few days. Sarah would have had children right to the end of her childbearing years, and a hardy woman might have had children to the age of 48-49. Since she had no children with Covington, I'd put her age at near 50 when she married him.
I'm still working on trying to put the Cavanaugh children in birth order and figure out their approximate ages.
Young Charles Cavanaugh would have known Jael (Harrison) Williams Johnson. Either she is his grandmother and he names a daughter after her, or he admires her and names a daughter after her. Of course, there is always the possibility that he named his daughter after his sister. An any event, all of the Jaels that I've come across in that region are connected to Jael Harrison.