
Patrick,
Back in 1999, I hired a Roscommon-based genealogist to research my grandmother (@Ann Cardiff). She provided me the following data about @Margaret Dwyer (Keher):
John Dwyer and Margaret Keher were married on July 21, 1881 (source: Civil Registration District of Athleague records). At the time, she was 22 and he was 27. That would put her birth year at 1859 or so.
The genealogist also sent me a copy of Form A of the Census of Ireland, 1901. That shows a Margaret Dwyer as the "Head of Family" and that her age was 53 on last birthday. That suggests a birth year around 1847. However, this could be a different Margaret Dwyer; the record shows three children living with her: Luke (age 27); Mary Jane (age 22); Patrick (age 18). None of those ages match up with the ones I have (and the other records show that Luke died as an infant).
Can you share the details of your census record? It seems a much closer match to the marriage record.