I think James is a bit older than he claims at his marriage, and later on. There is only one James Fairey (or variant) birth registered in St Neots district between 1837 and 1850, and this is in June Q 1839.
The Eatons Community site:
http://www.tsgcs.co.uk/escan/parishhistory.aspshows a James FAIRY s/o William and Eliza, baptised 9 June 1839
I think this couple are William FAREY and Eliza BALDOCK who married at Eaton S. in 1829.
A William Fairey aged 29 was buried Eaton S on 29 January 1841
1851 census
Eaton Socon
Eliza Fairey head W 39 Pauper Biggleswade
Ann Fairey daur 18 Lacemaker Eaton Socon
William Fairey son 16 Labourer Little Pain St. London
James Fairey son 11 Scholar Eaton Socon
Mary Ann Baldock visitor 6 Eaton Socon
1861 census
North Road, Eaton Socon
Eliza Fairey head W 50 Charwoman
Ann Fairey daur S 26 Dressmaker
James Fairey son S 21 ag Lab
John Fairey son 8
Mary A Fairey daur 15 Charwoman
All born Eaton Socon