Source = aged 21 at marriage in 1858.

Macosquin Presbyterian Church Baptismal Register has: Isabella Finlay, daughter of John and Mary Anne Finlay of Ballystrone, baptized 16/10/1829;  And yet she gave her age as 21 in her marriage certificate!!!!!

Source: SS
Isabella Finlay 10/16/1829-1866, age 36.

Also from the Pilot:
Name: Issabella Finley
Registration district: Coleraine
Record type: DEATHS
Registration date - quarter and year: 1866
Estimated birth year: 1830
Age: 36
Mother's surnames:
Film number: 101583
Volume: 1
Page: 393
Digital GS number: 4200215
Image number: 00088
Collection: Ireland, Civil Registration Indexes 1845-1958

Isabella Finlay died 2/24/1866 in Kiltinny, age 36, married, laborer's wife, pheumonia 8 days, certified, John Finlay, Ballystrone, present

Civil Birth Record
Name:    Male Finley    Date of Birth:    17-Feb-1866
         Registration Date:    1-Jan-0
Address:    Kiltinny    Parish/District:    ARTICLAVE
Gender:    Male    County    Co. Derry
Denomination:    Registrar District
Father:    Peter Finley    Mother:    Isabella Finley
Occupation:    Labourer    
Sponsor 1 /
Informant 1:    Mary Finley    Sponsor 2 /
Informant 2:    
Notes:

Male Finlay died 2/28/1866 Ballystrone, child of a laborer, debility since birth, uncertified, no medical attendant, John Finlay, Ballystrone present.