Allan and Adelia are in Monroe, Michigan in the 1850 census. He is born approx. 1823 (younger than you thought) and Adelia is born approx. 1838. There are four children with them; the eldest, Eliza is 11 or 12 (hard to read) which would make it hard for her to be Adelia's daughter, and even he would have been young to be her father. The next two, Mary and Mariah, are 7 and 4 and were born in Canada. The youngest Martha is born in Michigan.The same ages for Allan and Adelia roughly are given in the 1860 census in Huron County, Ohio.
His death index entry (familysearch.org) gives his age as 81 on his death in 1897 (born about 1816). You can order a copy of his obituary which may provide some more details:
Name: Allen Spratt Death Date: 1 Mar 1897 Death Place: Norwalk, Ohio Newspaper: Norwalk Daily Reflector, Norwalk, Ohio Newspaper Date: 03 Mar 1897 Newspaper Page: p. 3, col. 2 Years Indexed: 1882-1892 Newspaper Repository: Hayes Presidential Library - Fremont, Oh; Hayes Presidential Library- Fremont, Oh
The above info about the children would suggest that Allen was married before he married Adelia.