Hello Liz,
The age difference is ok, remember, John Henry was older than Edith Annie, and he would have made his age to match Ediths in any documents.
John Henry was baptised in 1855.
Edith Annie was baptised in 1869
Edith Annie remarried and lived a lot longer than John Henry.

and remember the Registry reply to you,

Yes its me again,
I asked at bmd to see if they had my john henry cain born douglas between 1863 to 1867 with father robert a carter,and robert was deceased by 1917,
the answer i got back was this,
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I haven’t found a baptism entry in the name of John Henry Cain, father’s name Robert, between the years you stipulated, I did find an entry for 30 March 1855 in Braddan, parents Robert Cain and Margaret Crowe, resident in Strang and father’s occupation a labourer.
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and don't worry about the Labourer bit.

Robert Cain was a Labourer for the Town Commissioners, his employers.
but his Job was a CARTER he drove and looked after the horse and cart.
John Henry would have known that and wrote on his marriage cert. CARTER.