Searching for William OBrien of Newcastle West, Limerick abt 1830-1880

I posted this to the general message board so I apologize if duplicate.I know, a William OBrien in Limerick is like a needle in a haystack, but thought I would post anyway to see if anyone can help.

My great-great grandfather was Michael William OBrien born abt 1850-52 in Newcastle West. His father was William, a farmer, who was still living in 1872 (this was according to Michaels Welsh wedding certificate).

Williams date of death is unknown. Michael William left Ireland abt 1870 for the Welsh coal mines, married and raised his family there before dying in 1904 in Trealaw.

Id like to uncover any records of Michaels birth/baptism from 1850-52, and also locate any records or existence of his father, William. His date of death is unknown, but again was sometime after 1872. The reason I am unclear about Michaels birthdate is that it changes from record to record. At his marriage in 1872 his age is 22 (b. 1850), but at his death in 1904 his age is 52 (b. 1852). Census records are the same with varying ages.

Ive never uncovered the name of Michaels mother, Williams wife. If naming conventions were followed I suspect she may have been Mary or Margaret. I believe he had at least one other son, James, who was older than Michael. The family was Catholic. Any help is much appreciated. Thanks, Jim OBrien, Seattle, WA