I am trying to work something out date wise on my tree and have come to a dead end. I see on various genealogy sites that THOMAS SHANAHAN and MARGARET STACK (1740) are quite well known and i'm hoping there are people on here who could help me out!

Here is what I have so far:

DANIEL SHANAHAN (b. 1680) from Irabeg, Lixnaw, Kerry had 2 children.

Daniel had 2 children with unknown

THOMAS SHANAHAN (1738) and John shanahan (1720)

THOMAS SHANAHAN (1738) m. MARGARET STACK (1740) and supposedly had 21 children.

one of these was THOMAS SHANAHAN (1845) m. MARGARET DOYLE (1845)

they had DENNIS SHANAHAN (1872)who m. JOHANNA MURPHY (1889) (my great great grandparents)

Now the issue is that the dates don't work out in terms of when shanahan and stack had their son Thomas, because that would have made the parents over 100years old. Am I missing a link? was there another Thomas in between them two?

I also cant find Dennis Shanahan on any census at all, he would have been about 29 at the time of the 1901. Found Johanna Murphy in 1901 but not in 1911. They had their first child in 1915 (my great grandmother margaret).

Does anyone have ANY information about this family. Really i'd take any help you could give.