Mulhern

I would Hi,  I'm looking for help finding a birth record and parent names for my great grandfather, John Mulhern.  On all documentation I have been able to find he consistently listed his birthplace as Fermanagh and my DNA ties me to that region, so I am confident that is accurate.  His age, however, differs on the various records.  I found his marriage record from October 9, 1887.  His age is recorded as 35.  His father was only listed as dead, no name given.  Based on that age, he would have been born around 1852.  Using that information, I found him in the 1871 Scottish census as a boarder working as a labourer with a recorded age of 20.  He also appears in the 1881 census in a different area of Scotland as a 29 year old boarder, again working as a labourer.  On that census, there is also a Patrick Mulhern, age 31, perhaps a brother or a cousin.  Those ages all match and I can see no reason why he would have lied about his age on those records.  By the 1891 census, John, his wife and children were living in Scotland and his age was listed as 28; in the 1901 census, he was 35, and when he emigrated to Canada in 1923, he was 55.  Since he supported his family as a general labourer, I assume it was advantageous for him to present himself as a younger man.  Any assistance or guidance in finding records would be greatly appreciated.