I really think at this point Joseph Rogers was older than his wife Susie. I have no idea how old he was, since all we have is his name on lists with Elisha in Roanne/Bledsoe Tennessee and the court records involving the Blackwater Salt Works.
It would be logical to assume they were above 21 in 1806 when Elisha is on the Tax list in Lee County. Thus they would be born no later than 1785.
I know that the only records for the wife of Doswell, Catherine shows her signing deeds in 1790ish, so it would be reasonable to assume she's the mother of Elisha and Joseph. Whether the age span works for all the children of Doswell is another thing, (20 years from Thomas in 1765 and Joseph born no later than 1785). Assuming an age of 15 (unusual but possible) in 1765, she would be 35 in 1785. If Catherine was 20, she would be 40 and still of childbearing age.