Margaret Biven's age at marriage would have been about 39/40 so perhaps thats why I haven't found any children.
I agree that the most probable Charles Paynter would be the one buried in 1801 which would have made him about 77 years old at death
Richard son of Charles Paynter and Mary Couch married Jane Bivens b 1758 St Ives daughter of John and Jane Bivens
I can find 2 Mary Paynters born to Richard and Jane Paynter (nee Bivens) but I dont seem to be able to find a death for the first Mary bp 07 May 1786 St Ives - The second Mary Paynter was bp 22 Apr 1793
The closest I can find in age is Mary Paynter who died Jan 1790 St Ives aged 9?