Date of Birth source: 1901 census - and also his death certificate which gives his age as 60 in 1902. 

 Date of Death from General Registry Office, Belfast - died of heart disease after 1 month's illness in Balteagh.  His wife Ellen McKeown was Present at Death, she also from Balteagh.

Date of Birth source: Old Age Pension Search results for Nancy Gibson.  1901 census gives her as 58 = 1843.  

She was informant at husband's death so lived beyond 1902.

This might be her:
Residents of a house 1 in Blagh (Ballylagan, Londonderry)
Surname    Forename    Age    Sex    Relation to head    Religion    Birthplace    Occupation    Literacy    Irish Language    Marital Status    Specified Illnesses    Years Married    Children Born    Children Living
Mc Curley    Mary Ann    51    Female    Head of Family    Church of Ireland    Co Londonderry    -    Read and write    -    Widow    -    29    6    5
Mc Curley    Ellen    19    Female    Daughter    Church of Ireland    Co Antrim    Shirt Maker    Read and write    -    Single    -    -    -    -
Mc Curley    Edward    13    Male    Son    Church of Ireland    Co Antrim    Scholar    Read and write    -    Single    -    -    -    -
Mc Keown    Eliza Ann    72    Female    Visitor    Presbyterian    Co Londonderry    -    Read only    -    Widow    -    -    -    


1914    McKeown    Ellen    70    1844    Coleraine    1;353    BG    
ORDER THIS ONE!  Probably my great great grandmother, Ellen Gibson - only Ellen in CRs    LDS Pilot
Coleraine Union, Coleraine; 23 April 1914, Infirmary, Coleraine; Ellen McKeown of Macosquin; Female; Widow; 70 years; House Keeper; Cerebral Haemorrhage. Two years, Cardiac Debility, Certified; Martha J Coleman, Occupier, Matron, Workhouse, Coleraine.
BG:  I think this means that she was in the hospital in Coleraine not the workhouse and that the registry office was in the workhouse.  In fact, Coleraine hospital WAS in the old workhouse.

Date of Birth source: Civil Registration birth entry in General Registry Office, Belfast.

Ireland, Civil Registration Births Index, 1864-1958 about Annabella M'Keown
Name:    Annabella M'Keown
Date of Registration:    1864
Registration district:    Coleraine
Birth Country:    Ireland
Volume:    6
Page:    471
FHL Film Number:    101041

Ireland, Births and Baptisms, 1620-1911 about Annabella Mckeown
Name:    Annabella Mckeown
Gender:    Female
Birth Date:    17 Mar 1864
Birth Place:    Articlave, Londonderry, Ireland
Father's Name:    James Mckeown
Mother's Name:    Ellen Gibson
FHL Film Number:    101085

Civil Birth Record
Name:    Annabella Mckeown    Date of Birth:    17-Mar-1864
         Registration Date:    
Address:    Letterloan    Parish/District:    ARTICLAVE
Gender:    Female    County    Co. Derry
Denomination:    Registrar District
Father:    James Mckeown    Mother:    Ellen Gibson
Occupation:    Weaver        
Sponsor 1 /
Informant 1:    Ellen Mckeown
Sponsor 2 /
Informant 2:    
Notes:

Death certificate shows she died of "Cardiac Failure Suddenly", and "of the labouring classes".  She resided in Ardvarness when she died.  John McClements, her son, of Ardvarness, was the informant.

After her death, I received some of Aunt Sadie's photographs and one was of a gravestone with this written on the back:
"Mum's
Mum and Dad
Englishtown
Cemetary
Near Coleraine"
The stone says:
"Erected
In Memory of
Samuel McClements
Ballywilliam
Who dies September 15th 1925
Aged 58 years
Also his wife
Annabella McClements
Who died June 20th 1925
Aged 63 years"
Ballywilliam is to the south of Ardvarness.

Source - Barbara Braswell using Vital records.  From the Births records in Derry Family History Centre: Index number: 11.480, 131, 20th July 1868 Kiltinney, William John, James McKeown Kiltinney, Ellenor McKeown, formerly Gibson, Labourer, Mary Law Present at Birth Kiltinney (she was PAB for 5 others on this page and was therefore likely to have been the 'midwife'.)

Civil Birth Record
Name:    William John McKeown    Date of Birth:    20-Jul-1868
         Date of Baptism:    1-Jan-0
Address:    Kiltinny    Parish/District:    ARTICLAVE
Gender:    Male    County    Co. Derry
Denomination:    Registrar District
Father:    James McKeown    Mother:    Ellenor Gibson
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    Mary Law