Hi
But it doesn't fit with his age on death, or his surname of Living not Pratt, or the name of Charles Pratt Living's wife - Polly, who outlived him by 21 years.
Death registration in New South Wales
1846 LIVING GEORGE C P AGE 53
Giving a birth year of circa 1793 which would just fit with this marriage
CHARLES PRATT LIVING
POLLY MILLEST
Marriage: 10 MAY 1792 Saint Paul Covent Garden, Westminster, London
LIVINGS, Charles Pratt
Christening Date:29 Apr 1764 Chertsey, Surrey
Father:John LIVINGS
Mother:Ann
But Charles Pratt Living had 4 male siblings all baptised in Chertsey (including one called George) and anyone of the older siblings, if they survived childhood and married (no burials in the Chertsey registers) could also presumably have chosen to name one of their sons after their brother/s, and other than Nathaniel you would expect them to have all married before Charles Pratt Living since they were older than him. Since Charles didn't marry until he was 29 even Nathaniel could have married before him.
Thomas 6/3/1754
George 18/3/1756 possible PCC will 1837 - gentleman of Vauxhall (Lambeth)
Richard 17/9/1758
Nathaniel 17/7/1767 possible on the 1841 census in Southwark aged 70 (1841 census adult ages rounded down to the nearest 5) a clerk, born Surrey.
Possible marriages
Thomas 1782 to Mary Adams , St Michael Brassishaw City of London
George 1786 to Jane Page (of St Mary Lambeth), All Hallows Lombard Street City of London
You might have expected if he was the son of Charles Pratt Living that Charles' will in 1817 would have made that clear or in Charles' widow's will.
Will of Polly Living, Widow of Chertsey , Surrey 19 January 1838 PROB 11/1889
Since it isn't obvious from Charles' will (though the Death Duty registers for the will would specify the relationship) it isn't at this point a simple explanation without further evidence from other Living wills such as Polly's and possibly as a longer shot's George's, the Death Duty registers or
'East India Company Mercantile Marine Baptism Certificates
Baptism certificates and certificates of age for marine officers 1780-1820: L/MAR/C/669-670. Both volumes are indexed'. since he served as a Captian in the company fleet.
All of which could help prove who his father was regardless of whether a baptism entry in a register is ever found.
Any of his uncles could have witnessed his marriage. The only brother that for sure was dead by 1823 was Charles.
Unfortunately the Surrey marriage index does not cover parishes in the metropolitan area of Surrey such as Southwark and Lambeth.
At this point the simpliest answer might be he is the son of brother George not Charles.
Regards
Valda