Hi Kevin,
Can I just clarify please?
I understand that you have a John Middleton b 1790 Broughton Astley marrying Martha Toone in 1811.
You also have John Middleton marrying Mary Woodburne in Broughton Astley. (date?)
Where does this couple fit in? Do you think these are the parents of John b 1790?
Do you have any siblings for your John? (who married Martha)
The Narborough baptism is very close to Broughton - perhaps the family lived between the two places and John thought he was born in Broughton which is what is recorded on the census? Perhaps he was born in Broughton but christened in Narborough?
I know that the mother of this John being Ann is a sticking point, so I wonder if the father John married twice - to Martha and to Ann? Alternatively there may have been a mistake on the Narborough register with mother's name being recorded as Ann rather than Martha.
This is where you may be able to do a bit of detective work to see if John and Martha or John and Ann baptised more children at Narborough. Also check the censuses to see if you can locate a John and Ann Middleton in the area. Then do the same search with the same couples in Broughton ...
The 1813 Narborough christening is the only one I can see. Others may have access to parish registers and may be able to offer alternative John Middletons.
Regarding John being 77 when he died ... A couple of years leeway regarding age at death is acceptable - ages given at death are not precise and not necessarily to be relied upon.