You are correct. Martin on this census, does fit the time frame and his occupation as Shepherd could possibly be turned into a farmer in 1911.
It is possible that the death source is incorrect, however the baptism link I posted does show 1874 thought the 1911 Census which I'm pretty confident of shows 1876.
This census shows his birthplace as Roscommon instead of Mayo, so that and, although his mother may have used a middle name, throws doubt in my eyes on the census.
In your opinion Deb, do you think that the baptism link I posted, could be the Martin on my tree?