DoB from aged 72 at death as recorded in the death notice in the Londonderry Sentinel.

DoD from death notice in the Londonderry Sentinel.

And Aghadowey parish church:
56 Boyd
Erected in memory of
John Boyd Junr, late of Collins, who departed this life, 22 June 1833, aged 27 years
also his father, William Boyd, who died 30 March 1848, aged 72 years 

DoB from age 88 in 1864 as per Civil Death record.

DoD from Civil Record of her death, where her residence looks like "Collause" but this must be Collins as it is in the Aghadowey District and there is no other possible townland.

Coleraine Chronicle Feb 26 1864:
Nancy Boyd - At the residence of her son in law, Mr. George Stewart, Collins, on the 20th inst., Nancy, relict of the late William Boyd, Collins, Aghadowey, aged 88 yrs.

DoB from age 27 at death in 1833 as per gravestone in Aghadowey CofI church.

DoD from gravestone in Aghadowey Church of Ireland church:
56 Boyd
Erected in memory of
John Boyd Junr, late of Collins, who departed this life, 22 June 1833, aged 27 years
also his father, William Boyd, who died 30 March 1848, aged 72 years

LG: "John [Collins] Boyd Jr, son of William & Nancy (Gage) Boyd, died 22 June 1833 ‘died when a young man, coming from church.’" 

Aged 81 at death in 1888 according to gravestone inscription.

His will is in the Irish Will calendar index:
Record Type Wills Calendars
Date of Death 17 May 1888
Year of Probate 1888
Name Kennedy Boyd
County Londonderry
Residence Killeague

Record Type Graveyard inscription
Date of Death 17 May 1888
Name Kennedy Boyd
Age 81
Parish Aghadowey
Church Aghadowey Church of Ireland
Civil District Coleraine
County Londonderry

From his gravestone as recorded at the Bann Valley site:
57 Boyd-Kennedy-Stewart-Gilmore
In memory of
Kennedy Boyd, died 17 May 1888, aged 81 years
his wife, Mary, died 16 July 1886, aged 71 years
their children
Nancy, died 10 February 1875, aged 29 years
Thos A., died 13 March 1878, aged 31 years
Mary, died 1 August 1864, aged 13 years
Wm. K., died 10 October 1893, aged 37 years
also Jane Stewart, wife of their son, William K. Boyd, died 3 February 1929, aged 75 years
Freddy Boyd, S.O.M.S, a glider pilot regiment, killed at Arnhem, 23 September 1944
Erected by William and Eliza Gilmore, Chase City, Virginia, USA

Aged 87 at death in 1896

DoD from LG

Name: Nancy Stewart
Registration District: Coleraine
Event Type: DEATHS
Registration Quarter and Year: Apr - Jun 1896
Estimated Birth Year: 1809
Age (at Death): 87
Mother's Maiden Name:
Film Number: 101599
Volume Number: 1
Page Number: 350
Digital Folder Number: 4200681
Image Number: 00116
Collection: Ireland, Civil Registration Indexes, 1845-1958

DoB from age 31 at marriage in 1850.  The History of the Boyd Family by William Phillip Boyd gives his DoB as 1817.

DoD from "History of the Boyd Family and Descendants with Historical Sketches." by William Phillip Boyd, 1912.

DoD from LG.