Dillon Family History Brick Wall

I've been trying for a long time to try and get my Irish ancestry further back but with no success, if someone could help I would be extremely grateful.

I've got back to a Patrick Dillon/Dillan who was born somewhere in Ireland (no one in my family knows whereabouts and no census returns or records provide any clues).

Patrick had a son, also called Patrick who was born in Ireland in about 1819-1822 (censuses give his date of birth as either 1821 and 1822 and his sons marriage certificate gives it as 1819) and moved to Manchester at some stage prior to his marriage in 1849 to an Ann Burns (also born in Ireland). I have not seen any evidence as of yet that Patrick Dillon/Dillan senior left Ireland, in fact I am inclined to believe that he stayed there as in 1849 Patrick junior's marriage certificate describes his Father as a farmer.

I have also discovered in the 1851 census that Patrick Dillon was living with his wife Ann at the same address as a Luke Dillon who was born in Ireland in about 1813 (from 1851 census) to 1816 (from 1841 census). Luke is shown on the census as being married to a Mary Dillon (also born in Ireland). Given that Luke and Patrick were living together it seems very likely that the two were related in some way.

A member of an online forum found the following baptism records that could potentially be the right ones for Patrick and Luke:

Name: Pat Dillon
Parish: Grangegeeth, Monknewtown, Dowth, and Rathkenny
Diocese: Meath
County: Meath
Baptism Date: 16 Oct 1821
Father's name: Patk Dillon
Mother's name: Biddy Gooden
Sponsor Witness 1: Pat Callaghan
Sponsor Witness 2: Ann Varden

Name: Luke Dillon
Parish: Grangegeeth, Monknewtown, Dowth, and Rathkenny
Diocese: Meath
County: Meath
Baptism Date: 27 Mar 1819
Father's name: Wm Dillon
Mother's name: Mary Gorman
Sponsor Witness 1: Austin Maury
Sponsor Witness 2: Ann Mullen
 

With nothing better to go on Meath seems quite likely given that the baptism records shows a Patrick Dillon born to a Patrick Dillon and a Luke Dillon born in the right sort of time period in the same county and parish. Luke's baptism date is 6 years out from the birth year he gives on the 1851 census and 3 years out from his 1841 census birth year (obviously there is the problem of ages being rounded down to the nearest 5 years in the 1841 census).

Is there any one who could help?