Thanks for the suggestion, Cathy. I have all the relevant wills I can find for the Houghton Conquest/Ampthill Armstrongs, including the will of Frances Thompson Armstrong, Charles Armstrong b 1712, John Armstrong b 1766 and Charles Armstrong b 1783.
I don't think there can be much doubt that the Charles Armstrong who married Sarah Larkinson was a son of Charles 1712.
Unless he was a completely new incomer to the county with his roots elsewhere, which is always a possibility. However, he named his children with family names, including Charles for his first son and Aolti Mira (another corruption of Althamia) for his first daughter, so this seems unlikely.
What I was trying to establish was whether he was Charles b 1750 to Charles 1712 and Althamia Priaulx (all of whose children allegedly died in infancy) or whether he was the Charles Armstrong alias Barton who is mentioned in Charles 1712's will as one of the sons of Mary his third wife, and was probably born in 1758-ish in Grafham, before their marriage, during their period of "fornication" (Mary had to do penance for said fornication!)
It seems one of those conundrums for which there is no resolution, as there is no indication anywhere of the age of the Charles Armstrong who married Sarah Larkinson, other than that he was over 21 when he applied for the marriage licence. There is no age on his probable burial entry in the NBI in 1800. If a birth year of around 1758 could be deduced, then that would be the answer, but it just doesn't seem possible from the information that can be gleaned.
The only clues are inconclusive -
1. He moved to Grafham with Sarah some time after the baptism of their eldest son Charles in HC in 1785, and they both were buried there; the move could be coincident with the death of Philip Armstrong in 1787 in Graffham. Said Philip had been left a farm in Graffham by his father Charles 1712, which was to remain in the possession of his morther Mary until he came of age. On his apparent death (in the NBI) whilst under age, the farm would have remained in the possession of his mother Mary. As John was well provided for with all the HC lands, Mary may well have handed over the Grafham lands to her son Charles.
2. Sarah's age at death in 1836 was 77, placing her birth year as 1759. IF they were about the same age, that would make a 1758/1759 birth for him possible. However, he died years before her in 1800, so could well have been older.
However, having now exhausted all lines of enquiry, I think I will abandon this one! My aim in tracing the "posh" Armstrongs was to see if there is any connection between them and my Armstrong family who originated in Riseley and seem to have seeded half of Bedfordshire with Ag Labs. There is no family relationship that I have been able to find.
The only documented link is that William of Haynes is mentioned as an executor and trustee in the will of John 1766. This link is probably because of the Ampthill Wesleyan chapel where they both baptised their children, and of which William was a warden. The other executor/trustee was Charles of Wootton, John's nephew.
There are other links via juxtaposition - e.g. members of the Wilstead/Goldington family ending up farming cheek by jowl with members of the Ampthill family - but nothing concrete.
No more to be done, methinks.