Where did Richard and Jane die, please? I'm struggling to locate their burials in Kimpton in 1800, the year you mention.
Jane Guyatt, widow, was buried 11 Nov 1801 aged 65. Is this 'your' Jane? This might put her birth date a little earlier than you indicated, if accurate.
A Richard Guyatt was buried in Kimpton 7 Jun 1792 aged 74. This would be the one born in 1717. Unfortunately there is no other Richard Guyatt buried in Kimpton that I have found.
Richard and Jane appear to have had the following children baptised in Kimpton:
James 9 Nov 1768 buried 3 Apr 1837 aged 68
Sarah 3 Feb 1771 buried 20 Jun 1796 age 25
Martha 6 Mar 1774
Jane 28 Dec 1776
Anne 25 Jun 1780
William 22 Aug 1784
I was intrigued to find these baptisms as well, parents Richard and Ann
Richard 7 Oct 1754 in Barton Stacey
John 27 Dec 1759 in Kimpton
Ann and baby John died soon after John was born, since both were buried on 10 Jan 1760. This Richard and Ann may have married as early as 1741, but I cannot find any other children or another likely marriage.
On the marriage record, Jane's surname is spelled with -b- . However, spelling was very erratic at this time and all possibilities should be considered.
I notice that you use the phrase 'supposed to be born' - this indicates that you perhaps don't have any hard evidence. It might be worthwhile to consider if your Richard was married before and was older than you think. How reliable is the source of the information?
Nell